Remove useless code
When sorting by due_date, display undefined values last

Markus' original patch was modified to simplify the code and reduce
duplication, fix a couple typos in comment text and reword the
commit message.

Fixes #16259
Remove DISTINCT clause from filter_get_bug_rows query

Fixes #16259 PostgreSQL error when filtering by due_date ASC
Follow-up fix for custom field names translations

In the case where we have multiple custom strings localized to the same
string, commit c174d88fc4f6a92e5bff0f7660688f1757c4cdaf would make it
impossible to distinguish them.

While this should not be a major issue in the bug history (as it doesn't
make sense to have more than one fields with a given localized name
within a given project), it is important that in custom field management
as well as project management pages custom fields are uniquely
identified with their "system" name to ensure there is no confusion.

This commit adds a new API function custom_field_get_display_name() that
will append the localized name to the field name, and which is called
from the above-mentioned pages.

Issue #12470

Conflicts:
	manage_proj_edit_page.php
Added new logo image without "mantis bug tracker" text

Square cropped copy of original mantis_logo.png
MantisCoreFormatting: Fix single-line fields html tags processing

Methods text() and formatted() Plugin sent a hardcoded 'true' parameter
to string_restore_valid_html_tags(), instead of using the method's
$p_multiline parameter.

Fixes #16342
MantisCoreFormatting: phpDoc corrections and improvements
MantisCoreFormatting: Remove code duplication

Method formatted() now calls text() instead of duplicating plain text
processing code

Bump plugin version to 1.0b

Fixes #16348
MantisCoreFormatting: Remove useless assignment

Fixes #16348, as per Roland Becker's comment
Whitespace fixes
Fix usage of tag_get_all for DBs not using Assoc fetch mode

This is a regression caused by implementation of issue #13446 (see
commit be3dde781523d4ecf11664eff0e6ec050993e044), which used a foreach
to iterate throught the ADOdb recordset returned by tag_get_all(),
instead of using MantisBT's db_fetch_array() function which takes care
of row association for DBs not supporting it natively.

Fixes #16340
Use correct threshold for display of Change status list+button

Fix for issue #15258 introduced a check for 'update_bug_threshold' to
prevent unauthorized users from changing issue status.

This was not the correct config setting to use, the right one is
'update_bug_status_threshold'.

Fixes #16376
Travis: only build for master and master-1.2.x

[skip ci]