<rdar://problem/12437929>

Providing a special mode of operator for "memory read -f c-str" which actually works in most common cases
Where the old behavior would provide:
(lldb) mem read --format s `foo`
0x100000f5d: NULL

Now we do:
(lldb) mem read --format s `foo`
0x100000f5d: "hello world"

You can also specify a count and that many strings will be showed starting at the initial address:
(lldb) mem read -c 2 -f c-str `foo`
0x100000f1d: "hello world"
0x100000f29: "short"



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@173076 91177308-0d34-0410-b5e6-96231b3b80d8