Specify a locale of en_US_POSIX to avoid localization problems in cer…

…tain situations, documented by Apple at https://developer.apple.com/library/ios/qa/qa1480/_index.html .  This was seen in testing with iOS, when using a British English current locale and choosing a 12-hour date preference in Settings.  NSDateFormatter actually rewrote the format to output "hh a" despite the request to print out "HH".  Using the POSIX locale ensures the output is not subject to user preferences, which is desired when printint out an ISO6801 compliant format.

ISO8601DateFormatter.m

@@ -713,7 +713,7 @@ - (NSString *) stringFromDate:(NSDate *)date formatString:(NSString *)dateFormat
 		unparsingFormatter.formatterBehavior = NSDateFormatterBehavior10_4;
 		unparsingFormatter.dateFormat = dateFormat;
 		unparsingFormatter.calendar = unparsingCalendar;
-        unparsingFormatter.locale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];
+		unparsingFormatter.locale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];
 	}
 
 	unparsingCalendar.timeZone = timeZone;
@@ -812,6 +812,7 @@ - (NSString *) weekDateStringForDate:(NSDate *)date timeZone:(NSTimeZone *)timeZ
 		unichar timeSep = self.timeSeparator;
 		if (!timeSep) timeSep = ISO8601DefaultTimeSeparatorCharacter;
 		formatter.dateFormat = [self replaceColonsInString:ISO_TIME_WITH_TIMEZONE_FORMAT withTimeSeparator:timeSep];
+		formatter.locale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];
 
 		timeString = [formatter stringForObjectValue:date];