Ox: Attribute Grammar Compiling System oxml2m4

- add 'branches' and 'tags' top level directories to the repository

- accidentally omitted from repository:
- used by 'libtool' to portably set library search paths
- lifted from Homebrew gettext v0.26

- update change summary log

- rewrite: Oxml2m4 is now a separately distributed package

- update to Automake & Aclocal version 1.18.1

./oxml2m4/parameter-table.cc
- in 'paramTable::insert ()', if the parameter name to be inserted is a duplicate, throw an 'insert_error' exception
- in 'paramTable::lookup ()', catch an 'std::out_of_range' exception and throw a 'lookup_error' exception

- document a defect: a parameter in a nested macro referencing a parameter of the enclosing macro fails

- update implementation due to change [r 53]
- minor source layout changes

- update generated files due to change [r 53]

- update Autoconf generated file due to change [r 53]