Make initenv work with trac 0.11 (fixes #369)

Fix two bugs (incorrect attribute, incorrect name of Exception) and
fixed the calling of trac 0.11.
Updated INSTALL file (refs #353)

Added pointer to Diagnostics, but also updated other sections.
Improve uWSGI documentation (closes #357)

In order to refer to the generated file, some code had to be moved around
a little bit. Improved other parts of the template a little bit as well.
Stop checking if feature is disabled (refs #348)

Not only are checks stopped if a feature (trac, svn, git) is disabled,
but also hide the checks in the template. Added bonus: show features disabled
as 'warning's, not 'error's.
Properly quote example commands

If a user is going to copy+paste these commands, they might run into trouble
with the angle brackets because in bash those are used for input/output
redirecting.