Add file rename functionality and tests

Add the function renameFile to our IO module, as both an error generating
and an error returning function.  This is supported by new qio runtime code
that makes use of the C function "rename".

Summary of changes:
modules/standard/IO.chpl - renameFile(err, oldname, newname) converts
   oldname and newname to c_strings before sending them to qio_file_rename,
   returning via err any error that may have occurred.  renameFile(oldname,
   newname) passes its arguments along to its sister function, and generates
   an I/O error if one occurred.
runtime/include/qio/qio.h
runtime/src/qio/qio.c - adds qio_file_rename to qio.  This method sends its
   arguments to rename and returns the qioerr version of errno if an error
   occurred.
test/io/lydia/rename/no_such_file - checks that the proper error is generated
   if the file to move did not exist.
test/io/lydia/rename/rename_file - checks that files are actually moved.