match: use _BASE_SIZE instead of magic value 4

Differential Revision: https://phab.mercurial-scm.org/D5351

mercurial/match.py

@@ -1212,7 +1212,7 b' def _buildregexmatch(kindpats, globsuffi'
         groupsize = _BASE_SIZE
         for idx, r in enumerate(regexps):
             piecesize = len(r)
-            if (piecesize + 4) > MAX_RE_SIZE:
+            if (piecesize + _BASE_SIZE) > MAX_RE_SIZE:
                 msg = _("matcher pattern is too long (%d bytes)") % piecesize
                 raise error.Abort(msg)
             elif (groupsize + piecesize) > MAX_RE_SIZE: