Convert the build process from CVS to git

Detect .git instead of CVS.  Use git-ls-files with git, else
$(srcdir)/sources.mk.  info/findsubj.pl now gets the info files as
arguments rather than from sources.mk.

Remaking info subjects doesn't quite work, but it was broken similarly
before.

src/scripts/cvsfiles.awk

@@ -1,24 +0,0 @@
-#!/usr/bin/awk -f
-# Find files under CVS control
-# FIXME Ignores CVS/Entries.log
-
-BEGIN {
-    FS="/";
-    if (ARGC == 1)
-	ARGV[ARGC++] = "CVS/Entries";
-    else {
-	for (i = 1; i < ARGC; i++)
-	    ARGV[i] = ARGV[i] "/CVS/Entries";
-    }
-}
-
-{ cwd = FILENAME; sub(/CVS\/Entries$/, "", cwd); }
-
-/^\// {
-    if ($3 !~ /^-/)
-	print cwd $2;
-}
-
-/^D/ && NF > 1 {
-    ARGV[ARGC++] = cwd $2 "/CVS/Entries";
-}