Correct a potential memory leak

Thanks to Ratany for drawing my attention to it.
Fix a conflict with the inventory offer button enum and the profile button's index
Set MeshMaxConcurrentRequests default back down to 32

The Lindens prefer it be this low and our users have found that lower is better lately.
Append the count of unread IMs to the IM session's name in the communicate button's flyout list

ShowUnreadIMsCount can be set false to turn this off
Fix for Issue 598: shortcut ctrl+alt+F1(disable UI) conflicts with linux (switch to other tty)

Reload personal setting overrides no longer has a shortcut.
On Linux, ctrl-shift-F# is now used instead of ctrl-alt-F#
On other platforms, nothing else changes.
Finish Singu TODO: Texture Save As from inventory menu.
Solve Issue 925: Add "Show on Map" to right-click menu for landmarks in inventory
Yet another attempt to solve Issue 929, bridge autodetach

This time we go through with the bridge attach but we setup a callback to detach once attachment process has gone through
Increment unread message count for IM floaters that are popped out but not focused.
Implemented decrement and distance_to for LLInstanceTracker::instance_iter and LLInstanceTracker::key_iter

Technically, both nested iterator classes in llinstance tracker should be derived from a common base implementation of boost::iterator_facade for std::maps(LLInstanceTracker::InstanceMap), they'd only need to implement dereference individually
Feature request: Add an option to open inventory folders in a new separate window
Satisfy Issue 613: TIme-stamp when viewing old notices in groups

To activate set LiruGroupNoticeTimes to true via debug settings
Depending on your date and time settings, you may need to resize the date column of the scroll list and hit refresh to see the times, alternatively, the tooltips will display the whole time always.
Merge from https://github.com/Lirusaito/SingularityViewer.git
made LLFloaterChat::onClickChatHistoryOpen() conform to
LLFloaterIMPanel::onClickHistory() in that it checks for the xantispam
rule "&-IMLogHistoryExternal"

Note: gViewerWindow->getWindow()->ShellEx(command); in these methods
apparently doesn't do anything on Linux and Mac.  I tried to figure
out what it is supposed to do without success.  If it runs 'command'
in a shell, this is a potentially very dangerous operation.