Ox: Attribute Grammar Compiling System oxml2m4

- 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]

- change '<elem>' to accept arbitrary expressions as the index value
- bump schema & package version to 1.3

- update generated file due to change [r 51]

- add explcit include for the 'gettext' M4suger macro library

- update Autoconf generated file due to change [r 49]