This commit modifies the GoT main branch to be able to compile it under linux.

Known to work against git-daemon and github Git server implementations. Tests by abieber, naddy, jrick, and myself. Man page additions reviewed by Lucas.

ok millert

got_error_fmt() could eventually replace got_error_path() which has already been used to construct errors with strings that are not actually paths... ok millert@

suggested by and ok millert

ok millert

ok tracey

this is for got push and got fetch, primarily ok stsp

semarie@ reported an error from go-git used by Cirrus CI: "57243613255d758e15b0f5ae1c960b970f0435f8: malformed mode (0100640)!" 'git fsck' has no problem with mode 0100640. But writing just the two most commonly used file modes should provide the best compatibility.

Commit IDs on histedit's temporary branch can change arbitrarily because the user may create new commits on this branch while editing past commits. So there is no point in trying to verify these IDs like we do during rebase. Add a test case which demonstrates the problem.