shelve: make unshelve be able to abort in any case

osx: explicitly build hg with /usr/bin/python2.7 This should help avoid creating a package that depends on a custom Python, as happened when I built a package for 3.8.

osx: correct comment about ordering of welcome page

osx: jettison outdated build instructions

commandserver: extract _cleanup() hook to clarify chg is doing differently This makes it clear that chg needs its own way to unlink closed socket file. I made a mistake in draft patches without noting the difference.

chgserver: drop repo at chgunixservice.__init__() Since it isn't expensive operation, we don't have to delay it to init().

chgserver: extract utility to bind unix domain socket to long path This is common problem of using sockaddr_un.

chgserver: narrow scope of chdir() to socket.bind() This helps extracting a utility function.

annotate: handle empty files earlier Rather than looping on funcmap and then checking for non-zero `l` continue if the result of fctx.annotate is empty.

context: eliminate handling of linenumber being None in annotate I could not find any use of this parameter value. And it arguably makes understanding of the function more difficult. Setting the parameter default value to False.