Test unicodesymbols for most supported input encodings with Kornel's addition to ctests.
Add required "forces" to unicodesymbols:
* utf8x does not support all characters supported by LyX
* several 8-bit encodings map characters to math-mode commands - force replacement in text-mode so that LyX can wrap them in \\ensuremath.
Fix a misalignment (wrong replacements) in the Cyrillic Unicode block.
Use \\mathscr for Mathematical Script characters in Mathematical Alphanumeric Characters (in line with the characters in other unicode blocks.
Specify non-TeX fonts that work in the source for documents that
fail with "missing characters" if compiling with "non-TeX fonts"=true.
(This does not interfere with the default output in any way.)
Add an exception to the conversion of "missing character" warnings into errors.
The PGF package deliberately uses the dummy font "nullfont" to suppress output.
Therefore, warnings about missing characters in "nullfont" are really only warnings.
Also updated the comment: "Missing character" warnigns are especially widespread
in XeTeX/LuaTeX but can also happen with "classical" 8-bit TeX.
Feel free to port this to branch.
