Fix the path to the user's appdata directory on Win Vista+.
Fix the path to the user's appdata directory on Win Vista+.

We were hard-coding the path to the user's Application Data directory, which
changed in Windows Vista. We now use the APPDATA environment variable, which
is guaranteed to point to the correct directory.

Fixes bug #1279

haosdent/rbtools,Khan/rbtools,clach04/rbtools,bcelary/rbtools,beol/rbtools,reviewboard/rbtools,clach04/rbtools_0.4.1,datjwu/rbtools,davidt/rbtools,beol/rbtools,beol/rbtools,blair/pkg-rbtools,davidt/rbtools,davidt/rbtools,halvorlu/rbtools,reviewboard/rbtools,datjwu/rbtools,1tush/rbtools,haosdent/rbtools,haosdent/rbtools,halvorlu/rbtools,Khan/rbtools,clach04/old_rbtools_0.3.2,reviewboard/rbtools,halvorlu/rbtools,datjwu/rbtools