hterm-vs-nassh: you can go your own way

This change splits hterm and nassh into separate directories,
and deals with the fallout.

The new nassh/ subdirectory contains Secure Shell specific code.
The hterm/ subdirectory is now dedicated to the hterm source.

libdot/bin/concat.sh has almost doubled in size to 380 lines.  It
now recognizes some additional "directives" that allow you to do
more than just include static files.  See the documentation at the
top of the file for details.

hterm/bin/mkdist.sh is a new script to create the version of the
hterm library intended for public consumption.  See the comment at
the top of this script for details.

hterm now has its own changelog, separate from Secure Shell.  This
first version of the public hterm library is marked as "1.0" and
starts with a fresh changelog.  The previous changelog is now in
the nassh/doc subdirectory.

The preferences editor lives in Secure Shell now.  Other hterm clients
will need to provide their own front end for hterm prefs for now.

The faq.txt and hack.txt files were moved over to nassh/doc/
directory, and hack.txt has been updated to match the new directory
layout.  I've left stub documents in hterm/doc to redirect people who
get there from existing links.

BUG=none
TEST=hterm_test.html, 66/66 tests passed, Secure Shell seems to work.

Change-Id: Idb969b53268baf741715ba4c972d7798d163184c
Reviewed-on: https://gerrit.chromium.org/gerrit/44444
Commit-Queue: Robert Ginda <rginda@chromium.org>
Reviewed-by: Robert Ginda <rginda@chromium.org>
Tested-by: Robert Ginda <rginda@chromium.org>
chomeapps/ssh_client/build.sh: get rid of pnacl-vs-nacl

The link that PNACL_SDK is set to
($SDK_ROOT/trunk.169649/naclsdk_linux.tar.bz2) is broken.  Let's not
rely on the trunk SDK anymore, and use the stable SDK which is readily
available on the native-client page.  It makes no differentiation
between NaCl and pNaCl, as the latter is default now anyway.  So,
update the link and remove all the NACL-specific code in the script.

BUG=None
TEST=build.sh works after applying the patch