newvers.sh takes upwards of 4 seconds to complete on trees checked out from github, due to searching the entire history for non-existent git-svn metadata. Similarly, if one does not check out notes, we again search the entire history for notes. That makes newvers.sh very slow for many github users.

To fix this in a fair way, limit the history search to the last 10K commit: if you're more than 10K commits out of sync, then you've forked the project, and our SVN rev is no longer very important to you.

Due to how git implements --grep in conjunction with -n, it has been removed for performance reasons (git does not seem to limit its search to the -n limit in this case, and takes just as long as it did before).