Merge branch 'maint'

Merge branch 'maint'

* maint:
  warnings: introduce -Wdeprecated in the usage info
  errors: prefix the output with "error: "
  errors: indent "invalid value for %define" context
  errors: indent "%define var" redefinition context
  errors: indent "symbol redeclaration" context
  errors: indent "result type clash" error context

Conflicts:
	src/complain.c
	src/muscle-tab.c
	src/reader.c
	src/symtab.c
	tests/conflicts.at
	tests/input.at
	tests/named-refs.at
	tests/output.at
	tests/skeletons.at