Updates bootstrap

Adds a THROW_EXCEPTION const
Force connect the db as otherwise mysql_escape fails
[enh] Readies AlterncTest for DbUnit testing
[enh] m_variablesTest is ready
[enh] Adds datasets for testing
[fix] SetUp and tearDown for tests should call parent props
[enh] db_mysql : adds exceptions
[enh] adds documentation and partially rewrites m_variables for testing

1. Does echo by default for helpers but makes it optional and returns result

2. Comments $variables = $this->variable_merge(array(),$arr_var['DEFAULT'][NULL]);
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as this failed to work here.