merge-recursive: Improve the error message printed when merge(1) isn't found.

Signed-off-by: Fredrik Kuivinen <freku045@student.liu.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-merge-recursive.py

diff --git a/git-merge-recursive.py b/git-merge-recursive.py
index 56c3641..b17c8e5 100755
--- a/git-merge-recursive.py
+++ b/git-merge-recursive.py
@@ -205,11 +205,16 @@
             orig = runProgram(['git-unpack-file', oSha]).rstrip()
             src1 = runProgram(['git-unpack-file', aSha]).rstrip()
             src2 = runProgram(['git-unpack-file', bSha]).rstrip()
-            [out, code] = runProgram(['merge',
-                                      '-L', branch1Name + '/' + aPath,
-                                      '-L', 'orig/' + oPath,
-                                      '-L', branch2Name + '/' + bPath,
-                                      src1, orig, src2], returnCode=True)
+            try:
+                [out, code] = runProgram(['merge',
+                                          '-L', branch1Name + '/' + aPath,
+                                          '-L', 'orig/' + oPath,
+                                          '-L', branch2Name + '/' + bPath,
+                                          src1, orig, src2], returnCode=True)
+            except ProgramError, e:
+                print >>sys.stderr, e
+                die("Failed to execute 'merge'. merge(1) is used as the "
+                    "file-level merge tool. Is 'merge' in your path?")
 
             sha = runProgram(['git-hash-object', '-t', 'blob', '-w',
                               src1]).rstrip()