before, if "mail.directory" was set, we'd assume the mail wasn't in the standard
default place, so we'd migrate Mail -> Mail5
now, we check if "mail.directory" == the default place. if so, we migrate
it like we would if it wasn't set.
Mail -> Users50/<profile>/Mail
to help do this, I added Equals() to the nsIFileSpec interface, to compare
two nsIFileSpec's, it does this by comparing the nsFileSpecs.
git-svn-id: svn://10.0.0.236/trunk@53396 18797224-902f-48f8-a5cc-f745e15eee43
