Add a new option 'linear_linestats' (default on).

When enabled, the lines of code statistics are collected from linear history.
The downside is that commits of feature long feature branches appear only at
the point where a merge commit is made.

If disabled (old behaviour), the problem is that if two branches contain the
same changes (for example, removal of same lines), the statistics get skewed.

Fixes line count statistics for this example repository:
git://github.com/septract/jstar.git

Thanks-to: Radu Grigore <radugrigore@users.sourceforge.net>

gitstats

 	'authors_top': 5,
 	'commit_begin': '',
 	'commit_end': '',
+	'linear_linestats': 1,
 }
 
 def getpipeoutput(cmds, quiet = False):
 		#  N files changed, N insertions (+), N deletions(-)
 		# <stamp> <author>
 		self.changes_by_date = {} # stamp -> { files, ins, del }
-		lines = getpipeoutput(['git log --shortstat --pretty=format:"%%at %%aN" %s' % getcommitrange('HEAD')]).split('\n')
+		extra = ''
+		if conf['linear_linestats']:
+			extra = '--first-parent -m'
+		lines = getpipeoutput(['git log --shortstat %s --pretty=format:"%%at %%aN" %s' % (extra, getcommitrange('HEAD'))]).split('\n')
 		lines.reverse()
 		files = 0; inserted = 0; deleted = 0; total_lines = 0
 		author = None
 			a['date_first'] = date_first.strftime('%Y-%m-%d')
 			a['date_last'] = date_last.strftime('%Y-%m-%d')
 			a['timedelta'] = delta
+			if 'lines_added' not in a: a['lines_added'] = 0
+			if 'lines_removed' not in a: a['lines_removed'] = 0
 	
 	def getActiveDays(self):
 		return self.active_days