Wrap ChamplainAdjustment

	* champlain/champlainmm.h: Add adjustment.h.
	* champlain/champlainmm/.gitignore: Ignore adjustment.*.
	* champlain/src/champlain_signals.defs: Add "changed" signal;
	add "lower", "upper", "value", and "step-increment"
	properties.
	* champlain/src/filelist.am: Add adjustment.hg.
	* champlain/src/adjustment.[hg|ccg]: New files.
	* tools/extradefs/generate_extra_defs_libchamplain.cc: Add
	CHAMPLAIN_TYPE_ADJUSTMENT and specific header.