This adds the capability to compile got-portable on FreeBSD.

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

Tweak man page. Factor out repeated code in if/else branches in send_gotconfig_remotes(). ok stsp@

Feature requested by naddy. ok naddy, who also suggested some tweaks that will arrive shortly

ok millert, naddy

Make use of this in 'got clone' to persist -R option arguments given on the command line in the cloned repository's got.conf(5) file.

Set fetch-all-branches in the got.conf(5) file created by 'got clone -a' in order to make a future 'got fetch' act like 'got fetch -a' by default.

ok tracey

POSIX says the limits defined there are available from <limits.h>, which almost all affected source files already included anyway. ok millert stsp

ok tracey