Fixed wrong path delimiter in exe finding

On Windows XP3 in git bash
git clone git@github.com:octocat/Spoon-Knife.git
cd Spoon-Knife
git gui
menu Remote\Fetch from\origin
error: cannot spawn git: No such file or directory
error: could not run rev-list

if u run
git fetch --all
it worked normal in git bash or gitgui tools

In second version CreateProcess get 'C:\Git\libexec\git-core/git.exe' in
first version - C:/Git/libexec/git-core/git.exe and not executes (unix
slashes)

after fixing C:\Git\libexec\git-core\git.exe or
C:/Git/libexec/git-core\git.exe it works normal

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: Evgeny Pashkin

compat/mingw.c

@@ -927,7 +927,7 @@ static void free_path_split(char **path)
 static char *lookup_prog(const char *dir, const char *cmd, int isexe, int exe_only)
 {
 	char path[MAX_PATH];
-	snprintf(path, sizeof(path), "%s/%s.exe", dir, cmd);
+	snprintf(path, sizeof(path), "%s\\%s.exe", dir, cmd);
 
 	if (!isexe && access(path, F_OK) == 0)
 		return xstrdup(path);