EXT-332: Added support for local currency estimates to the Buy L$

and Buy Land floaters.

We now check for a new estimatedLocalCost key from the XML-RPC server,
which provides the estimated cost in the user's local currency, e.g.,
"US$ 10.00" or "10.00 Euros". Note: the server is not currently
sending this information.

The previous codepath still exists and should be unaffected. That is,
we will continue to check for an estimatedCost key from the server with
a value specified in US cents. We give precedence to estimatedLocalCost
though and may want to remove this code once the international billing
server changes go live.

<lynx@lindenlab.com> HG: branch 'default' HG: changed
indra/newview/llcurrencyuimanager.cpp HG: changed
indra/newview/llcurrencyuimanager.h HG: changed
indra/newview/llfloaterbuyland.cpp HG: changed
indra/newview/skins/default/xui/en/floater_buy_land.xml