Merge branch 'nd/no-extern'

Noiseword "extern" has been removed from function decls in the header files. * nd/no-extern: submodule.h: drop extern from function declaration revision.h: drop extern from function declaration repository.h: drop extern from function declaration rerere.h: drop extern from function declaration line-range.h: drop extern from function declaration diff.h: remove extern from function declaration diffcore.h: drop extern from function declaration convert.h: drop 'extern' from function declaration cache-tree.h: drop extern from function declaration blame.h: drop extern on func declaration attr.h: drop extern from function declaration apply.h: drop extern on func declaration