If %TEMP% is set to a short path (e.g. "C:\LongDi~1") then tempname()
will return a file name that contains that short path. If that path is
later used as key for entry in s:temp_files dictionary, that entry won't
be found in BufNewFile,BufReadPost events because <afile> is expand()'ed
before it is used as a key for s:temp_files.
In the end, user gets cryptic error message about
"C:\LongDirName\VI12345.tmp.fugitiveblame" not being a git repository
when he tries to open a commit in Gblame window.
To workaround that we expand paths of temp files when adding entries to
s:temp_files. Also, because expand() can't expand short path if it
doesn't exist in the file system, we have to extract the directory part
and expand it separately.
4f24757df2