Since texinfo commit 6a5ceab6a48a4f052baad9f3474d741428409fd7, the
formatting functions, in particular begin_file, program_string and
end_file, are prefixed with format_, i.e. format_begin_file, etc.
This patch fixes building the documentation when texinfo 6.8, or
above, is used:
Unknown formatting type begin_file
at /usr/bin/makeinfo line 415.
Unknown formatting type program_string
at /usr/bin/makeinfo line 415.
Unknown formatting type end_file
at /usr/bin/makeinfo line 415.
(cherry picked from commit c980dd7a976635426f129417836251740e19b54b)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>