make it so we don't have to fully open a zip file to know it is

one..  This speeds up detection of large zip files..

[git-p4: depot-paths = "//depot/": change = 1129]

ZipStorage.py

@@ -213,6 +213,23 @@ class ZipChildDir(ZipItem, StorageFolder):
 	def __repr__(self):
 		return '<ZipChildDir: len: %d>' % len(self.pathObjmap)
 
+def tryTar(path):
+	# Try to see if it's a tar file
+	if path[-2:] == 'gz':
+		comp = tarfile.TAR_GZIPPED
+	elif path[-3:] == 'bz2':
+		comp = tarfile.TAR_BZ2
+	else:
+		comp = tarfile.TAR_PLAIN
+	return tarfile.TarFileCompat(path, compression=comp)
+
+def canHandle(path):
+	if zipfile.is_zipfile(path):
+		return True
+
+	#tar is cheaper on __init__ than zipfile
+	return tryTar(path)
+
 def genZipFile(path):
 	try:
 		return zipfile.ZipFile(path)
@@ -222,14 +239,7 @@ def genZipFile(path):
 		pass
 
 	try:
-		# Try to see if it's a tar file
-		if path[-2:] == 'gz':
-			comp = tarfile.TAR_GZIPPED
-		elif path[-3:] == 'bz2':
-			comp = tarfile.TAR_BZ2
-		else:
-			comp = tarfile.TAR_PLAIN
-		return tarfile.TarFileCompat(path, compression=comp)
+		return tryTar(path)
 	except:
 		#import traceback
 		#traceback.print_exc(file=log.logfile)
@@ -252,6 +262,7 @@ class ZipObject(FSObject, StorageFolder):
 		self.zip = genZipFile(self.FSpath)
 		hier = buildNameHier(self.zip.namelist(), self.zip.infolist())
 
+		print 'zip len:', len(hier)
 		doupdate = False
 		children = sets.Set(hier.keys())
 		for i in self.pathObjmap.keys():
@@ -288,7 +299,7 @@ class ZipObject(FSObject, StorageFolder):
 
 def detectzipfile(path, fobj):
 	try:
-		genZipFile(path)
+		canHandle(path)
 	except:
 		return None, None