Fix constraint dumping.

The string used in UIView+Introspector is an NSMutableString not an
NSString, so it should be modified in place rather than overwritten
with an NSString, to avoid a compiler warning.

Also fix a typo in the message.
Remove unnecessary __bridge.

This code is compiled without ARC, so the __bridge does nothing other
than cause a compiler warning.
Use DEBUG=1 in release builds, because CBIntrospect doesn't do anything
without this flag.
Merge branch 'remove-unused-bridge'
Merge branch 'fix-constraint-dumping'
Merge branch 'xcodeproj'