some nice ADC changes... (warning: minor backward compat breakage)

- support for ADCs with unchecked arguments
  - rsync, htpasswd, and svnserve gone from core; turned into ADCs

Backward compat breakage and fix: Please see documentation for details,
but if you're using gitolite to control rsync you will now need to setup
ADCs (admin defined commands), and install at least the new "rsync" ADC.

----

Thanks to Joey Hess (see commit prior to this) for forcing me to stop
being lazy and get this out of my long term todo list.

contrib/adc/htpasswd

@@ -0,0 +1,30 @@
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+
+BEGIN {
+    die "ENV GL_RC not set\n" unless $ENV{GL_RC};
+    die "ENV GL_BINDIR not set\n" unless $ENV{GL_BINDIR};
+    unshift @INC, $ENV{GL_BINDIR};
+}
+use gitolite_rc;
+use gitolite;
+
+die "$HTPASSWD_FILE doesn't exist or is not writable\n" unless -w $HTPASSWD_FILE;
+$|++;
+print <<EOFhtp;
+Please type in your new htpasswd at the prompt.  You only have to type it once.
+
+NOTE THAT THE PASSWORD WILL BE ECHOED, so please make sure no one is
+shoulder-surfing, and make sure you clear your screen as well as scrollback
+history after you're done (or close your terminal instance).
+
+EOFhtp
+print "new htpasswd:";
+
+my $password = <>;
+$password =~ s/[\n\r]*$//;
+die "empty passwords are not allowed\n" unless $password;
+my $rc = system("htpasswd", "-mb", $HTPASSWD_FILE, $ENV{GL_USER}, $password);
+die "htpasswd command seems to have failed with $rc return code...\n" if $rc;