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.
Merge branch 'master' into experimental

: get fix for history in local chat
removed obsolete debug output
experimental: "&-IMLongTab" and "&-IMShortTab" now work without
              messing with the log file names

This features is no longer experimental.
xantispam: fixed logic determining wether to use a long or a short tab
           for an IM session in the communications floater
xantispam: reset max tab width to be able to display long tabs after
           displaying a short tab
xantispam: leaving addFloater() untouched, using addFloaterSmallTab()
           instead
xantispam: added AntiSpamXtendedMaxTabLength debug setting to specify
	   the maximum tab length for when the &-IMShortTab rule is
	   applied
xantispam: increased the default for the
	   AntiSpamXtendedMaxCallsPer10Sec debug setting from 100 to
	   300