Some string speedups. Makes sony.com cached 11% faster.

        * kjs/ustring.h: Made it possible for UChar objects to be uninitialized, which
	gives a speed boost. Inlined CString's +=, UString's destructor, +=, and +.
        * kjs/ustring.cpp:
        (UString::UString): Optimize const char * version, which showed up
	heavily in performance analysis. Added new two-UString version, which
	makes the + operator fast.
        (UString::ascii): Remove thread safety changes. Change static buffer to remember
	its size, and to always be at least 4096 bytes long; that way we never have to
	reallocate unless it's for a long string. Also make code to extract the characters
	significantly faster by getting rid of two pointer dereferences per character.
        (UString::is8Bit): Avoid one pointer dereference per character.
        (UString::toDouble): Use ascii() instead of cstring() to avoid copying the string.

        * kjs/collector.cpp: Remove unneeded APPLE_CHANGES.
        * kjs/regexp.cpp: Remove ifdefs around some APPLE_CHANGES that we
	want to keep, because they just fix warnings.
        * kjs/value.h: Remove obsolete APPLE_CHANGES comment.

        * JavaScriptCore.pbproj/project.pbxproj: Project Builder decided
	to move a line around in the file.

WebCore:

        * force-clean-timestamp: JavaScriptCore headers changed that require a full build here.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@1791 268f45cc-cd09-0410-ab3c-d52691b4dbfc