Revert "Delete and re-add libpqxx-7.7.3 due to weird corruption."

This reverts commit e96515433d.

ext/libpqxx-7.7.3/tools/m4esc.py

@@ -0,0 +1,70 @@
+#! /usr/bin/env python3
+
+"""M4-quote text, for use as a literal in configure.ac.
+
+Produces M4 "code" which evaluates to the input text.
+
+It's not easy to read plain text from an input file in M4, without having it
+expanded as M4.  Sometimes all we want is literal text!
+"""
+from __future__ import (
+    absolute_import,
+    print_function,
+    unicode_literals,
+    )
+
+from argparse import ArgumentParser
+from sys import (
+    stdin,
+    stdout,
+    )
+
+
+def parse_args():
+    parser = ArgumentParser(description=__doc__)
+    parser.add_argument(
+        '--open', '-a', default='[[', help="Current open-quote symbol.")
+    parser.add_argument(
+        '--close', '-b', default=']]', help="Current close-quote symbol.")
+    parser.add_argument(
+        '--input', '-i', default='-', help="Input file, or '-' for stdin.")
+    parser.add_argument(
+        '--output', '-o', default='-', help="Output file, or '-' for stdout.")
+    return parser.parse_args()
+
+
+def open_input(in_file):
+    if in_file == '-':
+        return stdin
+    else:
+        return open(in_file)
+
+
+def open_output(out_file):
+    if out_file == '-':
+        return stdout
+    else:
+        return open(out_file, 'w')
+
+
+def escape(line):
+    return (
+        line
+        .replace('[', '@<:@')
+        .replace(']', '@:>@')
+        .replace('#', '@%:@')
+        .replace('$', '@S|@')
+    )
+
+
+def main(args):
+    with open_input(args.input) as istr, open_output(args.output) as ostr:
+        ostr.write(args.open)
+        for line in istr:
+            ostr.write(escape(line))
+            ostr.write('\n')
+        ostr.write(args.close)
+
+
+if __name__ == '__main__':
+    main(parse_args())