include codegen stuff into spec-file

[libt2n] / codegen / TODO

- remove support for LIBT2N_EXPORT_GROUP(group) (this will simplify the generator a lot)
- add option similar to gccs -MD (at the moment it is a fixed set of files generated and
  they are handled in the makefile snippet [codegen.make])

open questions:
- should projects using the codegen depend on installed version of ... or ship their own version?
- get rid of codegen-stubhead.hxx or include a "copy" in each project?
  first we said yes but now i say no because the lib depends on the libt2n headers anyway
- makefile snippet must work for builds outside of libt2n
  => some variables must be set by configure
  the variables which must be set:
	LIBT2N_CODEGEN="\$(top_builddir)/codegen/libt2n-codegen"
	LIBT2N_CLIENT_PCTEMPLATE="\$(top_srcdir)/codegen/clientlib.pc.in"
  => we store the variables in the .pc file of libt2n
- it would really be much nicer if the client lib includes would not depend upon boost serialization
  i thought a solution would be to provide this optionally by wrapping the corresponding includes in a #ifdef
  but this does not work since command.hxx is included which depends on boost serialization headers anyway
  => we do not provide this for now
- naming scheme?!
  perhaps generated group class should not be prefixed by cmd_group_