opal_get_version.m4: properly quote dir args

Make sure to surround directory variables with quotes so that they
function properly, even if there's spaces in the directory name.

While Open MPI doesn't generally support directory names with spaces,
this fix at least allows `autogen.pl` to complete successfully.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

config/opal_get_version.m4

@@ -83,9 +83,9 @@ m4_define([OPAL_GET_VERSION],[
             if test -d "$srcdir/.git" && test $git_happy -eq 1; then
                 if test "$srcdir" != "`pwd`"; then
                     git_save_dir=`pwd`
-                    cd $srcdir
+                    cd "$srcdir"
                     $2_REPO_REV=`git describe --tags --always`
-                    cd $git_save_dir
+                    cd "$git_save_dir"
                     unset git_save_dir
                 else
                     $2_REPO_REV=`git describe --tags --always`