#157 Small bug in unescapeChars()

[Wim Lewis]

I noticed a bug in XxUtil::unescapeChars(). Because of
the way it does the unescaping it can't tell whether a
given backslash is an escape character or an escaped
character in some circumstances, e.g., in the string
"foo\\narf" it'll replace the \n, instead of quoting the \\
as it should be. I've attached a patch which fixes this.

[Wim Lewis]

patch against src/util.cpp