largefiles: reuse hexsha1() to centralize hash calculation logic into it

This patch also renames argument of hexsha1(), not only for
readability ("data" isn't good name for file-like object), but also
for reviewability (including hexsha1() code helps reviewers to confirm
how these functions are similar).

BTW, copyandhash() has also similar logic, but it can't reuse
hexsha1(), because it writes read-in data into specified fileobj
simultaneously.

hgext/largefiles/lfutil.py

@@ -373,11 +373,8 b' def copyandhash(instream, outfile):'
 def hashfile(file):
     if not os.path.exists(file):
         return ''
-    hasher = hashlib.sha1('')
     with open(file, 'rb') as fd:
-        for data in util.filechunkiter(fd):
-            hasher.update(data)
-    return hasher.hexdigest()
+        return hexsha1(fd)
 
 def getexecutable(filename):
     mode = os.stat(filename).st_mode
@@ -398,11 +395,11 b' def urljoin(first, second, *arg):'
         url = join(url, a)
     return url
 
-def hexsha1(data):
+def hexsha1(fileobj):
     """hexsha1 returns the hex-encoded sha1 sum of the data in the file-like
     object data"""
     h = hashlib.sha1()
-    for chunk in util.filechunkiter(data):
+    for chunk in util.filechunkiter(fileobj):
         h.update(chunk)
     return h.hexdigest()