Add extra acceptable characters to CMICmdArgValFile (MI)

Summary:
Improve CMICmdArgValFile::IsValidChars to accept extra characters that can be in file name:
```
.'\"`@#$%^&*()_+-={}[]| 
```

Enable MiSyntaxTestCase.test_lldbmi_specialchars test.

All test pass on OS X.

Reviewers: abidh, emaste, zturner, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits, zturner, emaste, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D7859

llvm-svn: 230468