What version are you running?
2.5.7
What's the URL of the page containing the problem?
NO
What steps will reproduce the problem?

upgrade reviewboard by run the command:
easy_install -U ReviewBoard






What is the expected output? What do you see instead?
all the success, but I get the failed at last

the information in detail as following
What operating system are you using? What browser?
Ubuntu
Please provide any additional information below.
I get the output when run easy_install -U ReviewBoard, at last it failed
Searching for ReviewBoard

Reading https://pypi.python.org/simple/ReviewBoard/

Best match: ReviewBoard 2.5.15

Downloading https://pypi.python.org/packages/b7/ba/9f75e8dd6d5f96136de9ead2ec185f52a2738cb6667d100aa2595b9b2d1c/ReviewBoard-2.5.15-py2.7.egg#md5=f28abfb2a127ef09cba6164c0dd833ca

Processing ReviewBoard-2.5.15-py2.7.egg

removing '/usr/local/lib/python2.7/dist-packages/ReviewBoard-2.5.15-py2.7.egg' (and everything under it)

creating /usr/local/lib/python2.7/dist-packages/ReviewBoard-2.5.15-py2.7.egg

Extracting ReviewBoard-2.5.15-py2.7.egg to /usr/local/lib/python2.7/dist-packages

ReviewBoard 2.5.15 is already the active version in easy-install.pth

Installing rbext script to /usr/local/bin

Installing rbssh script to /usr/local/bin

Installing rb-site script to /usr/local/bin
Installed /usr/local/lib/python2.7/dist-packages/ReviewBoard-2.5.15-py2.7.egg

Processing dependencies for ReviewBoard

Searching for cryptography>=1.8.1

Reading https://pypi.python.org/simple/cryptography/

Best match: cryptography 2.0.3

Downloading https://pypi.python.org/packages/9c/1a/0fc8cffb04582f9ffca61b15b0681cf2e8588438e55f61403eb9880bd8e0/cryptography-2.0.3.tar.gz#md5=24cbdab3fda22be31dd3aef2808f5d2f

Processing cryptography-2.0.3.tar.gz

Writing /tmp/easy_install-WU67Ev/cryptography-2.0.3/setup.cfg

Running cryptography-2.0.3/setup.py -q bdist_egg --dist-dir /tmp/easy_install-WU67Ev/cryptography-2.0.3/egg-dist-tmp-0TQBGQ

Searching for cffi>=1.7

Reading https://pypi.python.org/simple/cffi/

Best match: cffi 1.10.0

Downloading https://pypi.python.org/packages/5b/b9/790f8eafcdab455bcd3bd908161f802c9ce5adbf702a83aa7712fcc345b7/cffi-1.10.0.tar.gz#md5=2b5fa41182ed0edaf929a789e602a070

Processing cffi-1.10.0.tar.gz

Writing /tmp/easy_install-WU67Ev/cryptography-2.0.3/temp/easy_install-iUwMCz/cffi-1.10.0/setup.cfg

Running cffi-1.10.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-WU67Ev/cryptography-2.0.3/temp/easy_install-iUwMCz/cffi-1.10.0/egg-dist-tmp-FtJaja

Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing libffi.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libffi' found
Package libffi was not found in the pkg-config search path.
Perhaps you should add the directory containinglibffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing libffi.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libffi' found
Package libffi was not found in the pkg-config search path.
Perhaps you should add the directory containinglibffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing `libffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

compiling '_configtest.c':

__thread int some_threadlocal_variable_42;
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -c _configtest.c -o _configtest.o

success!

removing: _configtest.c _configtest.o

compiling '_configtest.c':

int main(void) { __sync_synchronize(); return 0; }
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -c _configtest.c -o _configtest.o

gcc -pthread _configtest.o -o _configtest

success!

removing: _configtest.c _configtest.o _configtest

c/_cffi_backend.c:15: fatal error: ffi.h: No such file or directory

compilation terminated.

error: Setup script exited with error: command 'gcc' failed with exit status 1