Add machinery to output arbitrary unicode characters with LaTeX commands

Add machinery to output arbitrary unicode characters with LaTeX commands
read from a text file.

	* src/encoding.[Ch]

	(Encoding::latexChar): New, output a character to LaTeX
	(Encoding::validate): New, add needed preamble stuff for a character
	(Encodings::read): Read new unicodesymbols file
	(Encodings::isCombiningChar): New, is a character a combining char?

	* src/paragraph_pimpl.C
	(isEncoding): Delete, no longer needed
	(getEncoding): New, get the real encoding of a font
	(Paragraph::Pimpl::latexSurrogatePair): New, output a surrogate pair
	to LaTeX
	(Paragraph::Pimpl::simpleTeXBlanks): Use latexSurrogatePair if needed
	(Paragraph::Pimpl::simpleTeXSpecialChars): Ditto, and replace several
	hardcoded characters with a call of encoding.latexChar()
	(Paragraph::Pimpl::validate): replace several hardcoded characters
	with a call of encoding.validate()

	* src/support/debugstream.h
	(basic_debugstream::disable): New, disable the stream completely
	(basic_debugstream::enable): New, reenable the stream

	* src/lyx_main.[Ch]: Adjust to changes above

	* src/paragraph.C: Ditto

	* lib/unicodesymbols: New file with UCS4 -> LaTeX command mapping.
	It is far from complete yet, but contains most accents on latin
	characters.

	* lib/Makefile.am: add lib/unicodesymbols

	* development/scons/scons_manifest.py: ditto

	* development/tools/unicodesymbols.py: Helper script to update
	lib/unicodesymbols with new symbols

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@16920 a592a061-630c-0410-9148-cb99ea01b6c8