bug#13272: 24.3.50; `diff' output header line shows MS Windows root incorrectly

["Drew Adams" <drew.adams@oracle.com>]

I'm seeing this now in the very first line of my `M-x diff' output:
 
diff -c c\:/foo/simple.el c\:/foo/simple-patched-2012-12-24.el
 
The "c\:/" part is incorrect.  It makes no sense to write that.  It
should be written "c:/" - the `:' should not have a backslash in front
of it
 
The lines that follow the first line are, however, correct:
 
*** c:/foo/simple.el Mon Dec 24 13:48:06 2012
--- c:/foo/simple-patched-2012-12-24.el Mon Dec 24 14:00:56 2012
 
In GNU Emacs 24.3.50.1 (i386-mingw-nt5.1.2600)
 of 2012-12-18 on MS-W7-DANI
Bzr revision: 111265 eliz@gnu.org-20121218190556-x9wmq083vwecgu0f
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -Ic:/emacs/libs/libXpm-3.5.10/include -Ic:/emacs/libs/libXpm-3.5.10/src
 -Ic:/emacs/libs/libpng-dev_1.4.3-1_win32/include
 -Ic:/emacs/libs/zlib-dev_1.2.5-2_win32/include
 -Ic:/emacs/libs/giflib-4.1.4-1-lib/include
 -Ic:/emacs/libs/jpeg-6b-4-lib/include
 -Ic:/emacs/libs/tiff-3.8.2-1-lib/include
 -Ic:/emacs/libs/libxml2-2.7.8-w32-bin/include/libxml2
 -Ic:/emacs/libs/gnutls-3.0.9-w32-bin/include
 -Ic:/emacs/libs/libiconv-1.9.2-1-lib/include'