get back our old version string

src/tools/genVersionHeader.pl

@@ -91,7 +91,7 @@ elsif (-d '.git' || -f '.git') { # Git
     # v1-4-abcdef-dirty
     # is 4 commits after tag 'v1' with short hash abcdef
     # with uncommitted modifications
-    my $result = `git describe --always --tags --dirty --abbrev=20`;
+    my $result = `git describe --always --tags --dirty --long`;
     chomp $result;
     print "== git describe:\n$result\n==\n" if $opt_v;
     if (!$? && $result ne '') {