BMessageFormat: parse the pattern at construction

* Instead of parsing the pattern everytime Format() is called, parse it
only once when the object is created.
* Adjust all callers to make use of the feature and reuse the instance
as much as possible. This also allows calling B_TRANSLATE only once
instead of everytime the formatting needs to be done. We use either a
static instance (when the message pattern is constant) or a field (when
it is not known to be constant).
* Since the BMessageFormat instances are now reused, add locking to
avoid race conditions (ICU itself is thread safe, but the format pattern
is recreated when the locale is changed)

headers/os/locale/MessageFormat.h

@@ -9,10 +9,32 @@
 #include <Format.h>
 
 
+namespace icu {
+	class MessageFormat;
+	class UnicodeString;
+}
+
+
 class BMessageFormat: public BFormat {
 public:
-			status_t			Format(BString& buffer, const BString message,
-									const int32 arg);
+								BMessageFormat(const BString pattern);
+								~BMessageFormat();
+
+			status_t			InitCheck();
+
+			status_t			SetLanguage(const BLanguage& newLanguage);
+			status_t			SetFormattingConventions(
+									const BFormattingConventions&
+										conventions);
+
+			status_t			Format(BString& buffer, const int32 arg) const;
+
+private:
+			status_t			_Initialize(const icu::UnicodeString&);
+
+private:
+			status_t			fInitStatus;
+			icu::MessageFormat*	fFormatter;
 };