<rdar://problem/13404189>

Made the "--reverse" option to "source list" also be able to use the "--count". This helps us implement support for regexp source list command:

(lldb) l -10

Which gets turned into:

(lldb) source list --reverse --count 10

Also simplified the code that is used to track showing more source from the last file and line.




git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@176961 91177308-0d34-0410-b5e6-96231b3b80d8