Write QString replacement

[danielk]

Even in Qt4, QString is not thread-safe. We need to write an MString class with the capabilities of QString but without the constant segfaults.

[danielk]

(In [17846]) Refs #5311. Replaces most ascii()/utf8()/latin1() calls in libmyth with safer alternatives.

[danielk]

(In [17852]) Refs #5311. Eliminates all ascii()/utf8()/latin1() calls & most Q3CString instances in libmythupnp.

[danielk]

(In [17881]) Refs #5311. Fixes a number of instances of unsafe QString usage in MythTV.

[danielk]

(In [17886]) Refs #5311. Removes remaining QString::ascii() uses in mythtv proper; plugins still have not been addressed.

[danielk]

(In [17887]) Refs #5311. Gets rid of some Q3DeepCopy uses.

[danielk]

(In [17906]) Refs #5311. ascii()/utf8()/latin1()/local8Bit() removals and related fixes for mythplugins.

[stuartm]

See #4768

[jpbrock@…]

MString, a thread-safe replacement for QString

[danielk]

After converting a large number of files to Qt4, I don't think we need to introduce a new thread safe string class anymore. Assignments in Qt4 are really atomic and the very unsafe ascii()/utf8()/latin1()/local8Bit() functions were causing most of the remaining segfaults (and are now removed from the class). The remaining bugs are specific to certain classes used by multiple threads using QStrings without a mutex protecting them (ChannelBase for instance). Those errors should be addressed on a case by case basis as those classes will probably unsafely use any number of other variables, not just strings.