Remove set_include_path() calls

Since we know the full path to the files being included, it is not
necessary to change the include path.

Fixes #11549
Fixes #16850: Add config folder for customization files
Support including config file multiple times for custom_strings_inc.php
Update config_inc.php location in TestConfig
Update Travis to make config folder writable.
Fixes #17186: Remove  in favor of MantisTouchRedirect plugin.
Fixes #17185: Read-only access via soap api should be available to VIEWER level.
Changed chmod to be recursive for Travis.
Moved chmod to apply for all php versions not just 5.3.
Merged latest from master
Merged latest form master 2.
Rename all webservice configs options to webservice_* instead mc_*
Add support for MANTIS_CONFIG_FOLDER instead of MANTIS_CONFIG
Fixes with handling of global variables.
Fix include errors.
Relationship include fix.
Use config_get_global() for getting config_path in relationship_api.
Remove hard coded instances of config folder references
Fixed error where absolute_path was not defined.
Remove custom_strings_file config.