Creating temp file fails on Windows when $TMP contains '&'

[Ben Fritz]

C:\>cd tmp
C:\tmp>mkdir A^&B
C:\tmp>set TMP=%CD%\A^&B
C:\tmp>cd "%TMP%"
C:\tmp\A&B>gvim -N -u NONE -i NONE

:echo system('echo test')

E484: Can't open file C:\tmp\A&B\VIo82.tmp

C:\tmp\A&B>cd ..
C:\tmp>set TMP=%CD%
C:\tmp>gvim -N -u NONE -i NONE

:echo system('echo test')

test

See https://groups.google.com/d/topic/eclim-user/Ckf3lLnJ4tI/discussion where this came up. The solution for that eclim user was to set their TMP variable to not have the & symbol, but I think Vim should be able to handle this.