Auto-quote config values in config.c:store_write_pair()

Auto-quote config values in config.c:store_write_pair()

Suggested by Jakub Narebski <redacted> on the list.

When we send a value to store_write_pair(), make sure that the value
that gets read out matches the one passed in.  This means that for any
value that contains leading or trailing whitespace or any comment
character (# and ;), we need to surround it in quotes.

Signed-off-by: Brian Gernhardt <redacted>
Signed-off-by: Junio C Hamano <redacted>