Make sure to re-read the file data you can get from...

Make sure to re-read the file data you can get from OptionValueFileSpec::GetFileContents(...) when the file has changed.

This means you can set an expression prefix file with:
(lldb) settings set target.expr-prefix /tmp/to/prefix.txt

And you can run an expression and modify your expression prefix file in another editor without having to type:

(lldb) settings set target.expr-prefix /tmp/to/prefix.txt

again...

<rdar://problem/12155942> 

llvm-svn: 231535