Merge branch 'ls/p4-keep-empty-commits' into maint

"git p4" used to import Perforce CLs that touch only paths outside the client spec as empty commits. It has been corrected to ignore them instead, with a new configuration git-p4.keepEmptyCommits as a backward compatibility knob. * ls/p4-keep-empty-commits: git-p4: add option to keep empty commits