Back-patch "Only quote libpq connection string values that need quoting."

Back-patch "Only quote libpq connection string values that need quoting."

Back-patch commit 2953cd6d17210935098c803c52c6df5b12a725b9 and certain
runPgDump() bits of 3dee636e0404885d07885d41c0d70e50c784f324 to 9.2 and
9.1.  This synchronizes their doConnStrQuoting() implementations with
later releases.  Subsequent security patches will modify that function.

Security: CVE-2016-5424