mlpl ParsableString: Fix segmentation fault caused by user-supplied non-ascii strings.

In SeparatorChecker, an array (m_separatorArray[]) is used for checking
if each character is one of separators or not.

The array index is converted from char. Singedness of char is
implementation-defined and non-ascii (e.g. utf-8) characters may be
evaluated as negative values.

In fact, we screwed up if a user set up an "action" with non-ascii
string (ああああ.sh for example).

Note that we can assume that all separators are ascii characters,
however, user-supplied string must not result in accessing the array
out of bounds.

Signed-off-by: YOSHIFUJI Hideaki <hideaki.yoshifuji@miraclelinux.com>
Merge pull request #831 from project-hatohol/fix-segv-in-mlpl-parsable-string-20141207

mlpl ParsableString: Fix segmentation fault caused by user-supplied non-ascii strings.
[testParsableString] Add a test for readWord() against UTF-8 string