Fix travis build errors for PostgreSQL

The errors were caused by executing queries with params in wrong order.

To fix the problem, this commit adds Database API functions to push the
current parameter number onto a stack and pop the value after query
execution, allowing build of multiple queries concurrently.

The caller can call db_param_push() when needed prior to starting the
build of a new query while another one is still pending execution.
db_query_bound() will call db_param_pop() after running the query.

Fixes #14398
Move parameter count management to a class

The MantisDbParam class handles the logic for:
- assignment of parameters, db_param() calls
- push onto stack, db_param_push() calls
- pop stack
Update ADOdb to latest 5.19dev
Travis before script: use variable for port number

This facilitate local debugging using PHP built-in web server when there
is another web server running on default port 80.
Travis: stop ignoring build failures for PostgreSQL

[skip ci]