Add THROW_[MF]ALERT[EC] (AIArgs, AIAlert, AIAlertCode, AIAlertPrefix, AIAlertLine)

A system to throw errors that allow for easy error reporting to the user
by showing a translated pop-up alert box with the error message.

The messages use strings.xml for translation and allow the usual
replacement args (ie [FILE] is replaced with a filename).

The exceptions can be cascaded, by adding more (translated) text
when caught and then re-throwing the result.

Macros are being used to support adding a function name prefix
to a message of the current function that the exception is thrown
from.

The syntax is:

  <macro>(<line>);		to show 'line'
  <macro>(<alert>, <line>);	to append 'line' to a caught alert.
  <macro>(<line>, <alert>);	to prepend 'line' to a caught alert.

  where <macro> is one of:
  THROW_ALERT, THROW_MALERT, THROW_FALERT, THROW_FMALERT,
  THROW_ALERTE, THROW_MALERTE, THROW_FALERTE, THROW_FMALERTE, where
  M = modal, F = Function name.
  and where <line> is one of:

  <xmldesc>
  <xmldesc>, AIArgs<args>

  where <xmldesc> is a string literal that will be looked up
  in strings.xml, and <args> is:

  (<key>, <replacement>)[<args>]

  There are more variations of the macros to throw an arbitrary
  class (append _CLASS), include an int code (append C) or
  to store the current errno as code (append E).

  For example, THROW_MALERTC(code, ...), or THROW_FALERT_CLASS(Foobar, ...),
  where the ... is the same as for the macros above.

Documentation and example usage has been added to aialert.h.

indra/llui/llnotificationsutil.cpp

@@ -30,6 +30,11 @@
 #include "llsd.h"
 #include "llxmlnode.h"	// apparently needed to call LLNotifications::instance()
 
+LLNotificationPtr LLNotificationsUtil::add(AIAlert const& alert, unsigned int suppress_mask)
+{
+	return LLNotifications::instance().add(alert, suppress_mask);
+}
+
 LLNotificationPtr LLNotificationsUtil::add(const std::string& name)
 {
 	return LLNotifications::instance().add(