Fix modman for "auto-append-gitignore"

magento-hackathon/magento-composer-installer has an option
"auto-append-gitignore" which adds the contents of modman to .gitignore
for you . However, it does this blindly and using a wildcard on a
directory causes the entire directory to be added, in this case the
/app/code/community/Varien/ directory
Merge pull request #2 from rbrown/fix-modman

Fix modman for "auto-append-gitignore"