Documentation: making default value more obvious

$g_file_upload_method as an example.

Issue #16610
Fixes #16767: upgrade_unattended script is no longer working.
In an attempt to get MantisBT / MantisTouch redirection to work better on mantishub.com several issues were fixed.

Fixes #16768: Default mantistouch_url correctly when MantisTouch is installed in 'm' subfolder.
Fixes #16769: MantisTouch redirect can break soap api based on user agent sent.
Fixes #16770: Redirect from MantisBT issue to MantisTouch should go to the same issue page on MantisTouch.
Update log_event to use sprintf to apply additional parameters to string arguments
If an error occurs, and we are running from the client sapi api, just display the raw error on a new line and do not attempt to add any html formatting
limit_email_domains: Allow users to be locked to a choice of multiple email domains, instead of a single domain. For example:

 $g_limit_email_domains		= array( 'users.sourceforge.net', 'sourceforge.net' );

would allow people to sign up using email address @users.sourceforge.net or @sourceforge.net only
1) Always treat debug email address as a string (this makes phpdoc/clients that try to do type checking less confused)

2) Use PHP's own email validation routines (available since php 5.2)
Spelling Corrections
Performance optimisation for users not using email send via cron jobs and using php-fpm - generally this would be nginx users. Windows(IIS) fastcgi does not use php-fpm.
Remove Twitter code from Mantis Core that no longer works due to twitter's deprecation of username passwords
Retain inherited category when moving issue to sub-subproject

Prior to this, the category would be reset to default when moving an
issue more than one level down the project hierarchy, even though all
subprojects are set to inherit categories from their respective parents.

Thanks to lukasd for identifying the issue and providing the fix.

Fixes #16182
Fix #16810: $s_os in custom_strings_inc.php partially ignored
Remove usage of undefined constant ERROR_TWITTER_NO_CURL_EXT

Commit cd3e0ed21fb39577af3cb48b941be4001b659dd5 removed Twitter code but
not the usage if constant ERROR_TWITTER_NO_CURL_EXT in language file.
Fix #11785: Comment for access_compare_level in access_api.php is bogus
Prompt user with message on create project page on first login

When user logs in and there are no projects, they are redirected to create project page.  Show a message to users to create a project similar to one shown on login when the administrator user name and password are the default.
Remove main page from main menu when news feature is OFF

The main page was really designed to include the news which has been deprecated for a while.  Hence, the main page is useless for most users.  This change hides it unless the news feature is ON.

This is until the news feature is completely removed.
Fixes #16833: Remove show_avatar_threshold config option.
Revise footer to be less verbose and more like 1.2.x

- Don't show administrator email on login page.
- Show copyright years independent of show_version given that they currently are from 0 to today's year, so no disclosure of versioning anyway.
- User copyright message shows up after our copy right and before contact administrator message.
- Use much brief message for contacting administrator.  Remove usage of the word "us".
Replace email_* calls with raw email_generic calls. This is to try and make a shorter patchset in a bit ;)
Port a potential database corruption fix in the installer to 1.x from 2.x branch.

When converting dates, abort if the old value has already been converted to an integer from a database timestamp.
This avoids potentially wiping out dates quietly within the database.