Add a snippet to remove LangSys from DFLT script

Such fonts violate the spec and OTS rejects them, this snippet should
help quickly fixing such fonts.

Snippets/fix-dflt-langsys.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python
+
+import argparse
+import logging
+import os
+import sys
+
+from fontTools.ttLib import TTFont
+
+
+def ProcessTable(table):
+    found = set()
+
+    for rec in table.ScriptList.ScriptRecord:
+        if rec.ScriptTag == "DFLT" and rec.Script.LangSysCount != 0:
+            tags = [r.LangSysTag for r in rec.Script.LangSysRecord]
+            logging.info("Removing %d extraneous LangSys records: %s",
+                         rec.Script.LangSysCount, " ".join(tags))
+            rec.Script.LangSysRecord = []
+            rec.Script.LangSysCount = 0
+            found.update(tags)
+
+    if not found:
+        logging.info("All fine")
+        return False
+    else:
+        for rec in table.ScriptList.ScriptRecord:
+            tags = set([r.LangSysTag for r in rec.Script.LangSysRecord])
+            found -= tags
+
+        if found:
+            logging.warning("Records are missing from non-DFLT scripts: %s",
+                            " ".join(found))
+        return True
+
+
+def ProcessFont(font):
+    found = False
+    for tag in ("GSUB", "GPOS"):
+        if tag in font:
+            logging.info("Processing %s table", tag)
+            if ProcessTable(font[tag].table):
+                found = True
+            else:
+                # Unmark the table as loaded so that it is read from disk when
+                # writing the font, to avoid any unnecessary changes caused by
+                # decompiling then recompiling again.
+                del font.tables[tag]
+
+    return found
+
+
+def ProcessFiles(filenames):
+    for filename in filenames:
+        logging.info("Processing %s", filename)
+        font = TTFont(filename)
+        name, ext = os.path.splitext(filename)
+        fixedname = name + ".fixed" + ext
+        if ProcessFont(font):
+            logging.info("Saving fixed font to %s\n", fixedname)
+            font.save(fixedname)
+        else:
+            logging.info("Font file is fine, nothing to fix\n")
+
+
+def main():
+    parser = argparse.ArgumentParser(
+            description="Fix LangSys records for DFLT script")
+    parser.add_argument("files", metavar="FILE", type=str, nargs="+",
+                        help="input font to process")
+    parser.add_argument("-s", "--silent", action='store_true',
+                        help="suppress normal messages")
+
+    args = parser.parse_args()
+
+    logformat = "%(levelname)s: %(message)s"
+    if args.silent:
+        logging.basicConfig(format=logformat, level=logging.DEBUG)
+    else:
+        logging.basicConfig(format=logformat, level=logging.INFO)
+
+    ProcessFiles(args.files)
+
+if __name__ == "__main__":
+    sys.exit(main())