Merge pull request #5 from fjammes/master

setting exec right on eups_setup at configure time
BUGFIX on retrieving SHA1 id for a tag :
- 'git checkout -q GITREV -- ups' returns the last commit id which contains a
ups/ dir similar to the one in GITREV, this can be incorrect if ups/ content
hasen't changed in commit subsequent to GITREV

git rev-parse --verify GITREV is better.