Add a "--reverse" or "-r" option to the "list" with no options command. This...

Add a "--reverse" or "-r" option to the "list" with no options command.  This will list backwards from the
last source point listed.
Also fix the setting of the default file & line to the file containing main, when you do a plain "list".

<rdar://problem/12685226>

llvm-svn: 171945