Fixed project 'active days' counting.

Commits in projects with lots of activity and authors don't happen
chronologically (patches are accepted later etc), so the counting was messed up
for them (git.git for example).

gitstats

 		self.first_commit_stamp = 0
 		self.last_commit_stamp = 0
 		self.last_active_day = None
-		self.active_days = 0
+		self.active_days = set()
 
 		# timezone
 		self.commits_by_timezone = {} # timezone -> commits
 			# project: active days
 			if yymmdd != self.last_active_day:
 				self.last_active_day = yymmdd
-				self.active_days += 1
+				self.active_days.add(yymmdd)
 
 			# timezone
 			self.commits_by_timezone[timezone] = self.commits_by_timezone.get(timezone, 0) + 1
 		f.write('<dt>Project name</dt><dd>%s</dd>' % (data.projectname))
 		f.write('<dt>Generated</dt><dd>%s (in %d seconds)</dd>' % (datetime.datetime.now().strftime(format), time.time() - data.getStampCreated()))
 		f.write('<dt>Generator</dt><dd><a href="http://gitstats.sourceforge.net/">GitStats</a> (version %s)</dd>' % getversion())
-		f.write('<dt>Report Period</dt><dd>%s to %s (%d days, %d active days)</dd>' % (data.getFirstCommitDate().strftime(format), data.getLastCommitDate().strftime(format), data.getCommitDeltaDays(), data.getActiveDays()))
+		f.write('<dt>Report Period</dt><dd>%s to %s (%d days, %d active days)</dd>' % (data.getFirstCommitDate().strftime(format), data.getLastCommitDate().strftime(format), data.getCommitDeltaDays(), len(data.getActiveDays())))
 		f.write('<dt>Total Files</dt><dd>%s</dd>' % data.getTotalFiles())
 		f.write('<dt>Total Lines of Code</dt><dd>%s</dd>' % data.getTotalLOC())
 		f.write('<dt>Total Commits</dt><dd>%s</dd>' % data.getTotalCommits())