This simplifies a number of escape sequences.
The generated file to configure the man page was split up a bit further:
- code that extracted the GNC_VCS_REV_Y_M from gnc-vcs-info.h was spun out
into its own function that now sets all parameters in gnc-vcs-info.h
as environment variables.
- this function is now invoked by configure-manpage.cmake to extract
the date to insert into the manpage.
- the manpage in addition now shows the full date rather than only
yyyy-mm. This is how man itself does it as well.
