Use full rails server command in Vagrantfile docs
Fix Vagrantfile customisation docs

Used the local constant rather than the env var required
Reposition test, development group

Develop seems to be a debugging group so should
take lowest visual precedence.
Move gems to appropriate Gemfile Groups

Don't install things we don't need in the given environment.

Mainly an attempt to speed up CI builds somewhat:
http://docs.travis-ci.com/user/languages/ruby/#Speed-up-your-build-by-excluding-non-essential-dependencies
Rename develop Gemfile group to debug

Develop is too similar to development to mean anything different.
Don't install debug gems for CI
Merge branch 'vagrantfile-docs' into rails-3-develop
Merge branch 'update_gemfile' into rails-3-develop
Work around bug#77932 in pdftohtml

Sometimes pdftohtml will generate thousands of images when converting an
image embedded in a PDF. This causes a request spike when a user tries
to view the converted PDF as HTML.

See https://bugs.freedesktop.org/show_bug.cgi?id=77932 for the bug
report.