housekeeping: Make some functions public to allow debugging
housekeeping: Create test program for bug 730223

$ mkdir /tmp/gsd-purge-temp-test
$ mkdir /tmp/important/
$ touch /tmp/important/dont-delete.txt
$ ln -s /tmp/important/ /tmp/gsd-purge-temp-test/
$ ls -l /tmp/gsd-purge-temp-test/
0 lrwxrwxrwx. 1 hadess hadess 15 May 16 16:41 important -> /tmp/important/
$ ./gsd-purge-temp-test
<ctrl+c>
$ ls -l /tmp/gsd-purge-temp-test/
total 0
$ ls -l /tmp/important/
total 0
housekeeping: Fix warnings when info cannot be gathered