Windows sessions ignore drive letters

[dhruvasagar]

One follow up observation and an additional problem based on the following correspondence table:

Windows Dir	ignore_string
c:\TEMP	"c:/TEMP"
d:\TEMP	"d:/TEMP"

On Windows machines, it looks like vim-prosession does not care about the drive-letter, and saves the session into %TEMP.vim regardless of where GVIM is launched.