Guile 1.8 fixes for r23556 and r23557

- guile 1.8 doesn't need the swig patch
- make sure all swig interface files include guile-mappings.h
  for the *utf8_string to *locale_string mappings
  but only load it when building guile modules

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23559 57a11ea4-9604-0410-9ed3-97b8803252fd
SWIG version updates

- move the swig version check after the guile checks
  this allows us to check for a different version of swig
  based on the guile version that was detected
- use more recent autoconf macros for swig (from the autotools archive)
  this give us more flexible error reporting

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23560 57a11ea4-9604-0410-9ed3-97b8803252fd