Fixed an amount parsing error in expressions

Fixes #379
polib is now on PyPI
Moved credits into a language-independent file
Added Nelson Brown to the credits
Changed copyright year to 2014
Fixed copyright year
v2.7.2
Fixed build script for OS X
Fixed wrongly named credit.tmpl files in doc
Removed bogus symlinks in help folder
Added 'trusty' to the list of supported ubuntu releases
Catch Sphinx SystemExit when building help

In a recent Sphinx release, it started calling `sys.exit()` and that
caused our whole build process to exit prematurely.
Modernized bootstrapping code