Fixes #8207 mantis_project_hierarchy_table allows duplicate rows

This fixes a possible issue where the project hierarchy table can contain duplicate entries, by adding a unique index on the table
Fixes #17246: Date custom fields can't store dates pre-1970. - part 2
Travis: only use Apache as web server

Workaround for build errors with PHP built-in web server since
30-Apr-2014 [1].

[1] https://github.com/travis-ci/travis-ci/issues/2235
Travis before_script add DB_TYPE

Since PHP >= 5.5 has deprecated mysql driver, we use mysqli instead
Travis before script: PORT was defined but not used
Document ability to display status on bug_report_page.php

Fix for issue #14678 omitted to amend the comment block in
config_defaults_inc.php as well as the documentation.

Fixes #17289
Fix query execution error in user_get_accessible_subprojects()

Because of missing '!' operator, the parameters array did not have
enough values for the query when $p_show_disabled = true.

Regression introduced by 927706b3311407712ee16b9be71f56a974683d73
Tweak messages
Fix i18n issue in login_page.php

Sentence parts should now be glued together. Instead, I've created full
sentences. They are combined using a word separator.
Use "code" tags for configuration text
Use MantisBT, fix grammar and stop yelling
Localisation updates from https://translatewiki.net.
Localisation updates from https://translatewiki.net.
Update supported languages

Also remove an inline tab I spotted.
bug_report.php: fix warning when not using attachments

When attachments are not used, 'ufile' is not defined, so $t_files
becomes NULL (line 150) causing the 'Invalid argument supplied for
foreach' warning.

Fixes #17322
Fix #17324: remove var_dump()
Issue #17322: apply same logic in bug_file_add.php
Provide a description for unknown error types
Separate error type from description with colon

This makes the error message look more like standard PHP errors.
Exit with an error code of 1

This allows the calling script to respond in an appropriate manner in
case an error occurs.