Server: Fix client->server CB xfer issue w/Qt apps

Validating the timestamp in vncConvertSelection() was too strict, since
ProcConvertSelection() doesn't do that, and some applications expect the
more lenient behavior.

Based on:
TigerVNC/tigervnc@dfc2001

Fixes TurboVNC#158

Tunnel.java: Remove unused import

Detected by checkstyle.java.  This should have been part of
e85e705.

Fix continuous integration of pull requests

- Travis doesn't set the $encrypted_* variables for PRs, so disable GPG
signing when building a PR (artifacts aren't deployed for PRs anyhow,
and even if they were, I wouldn't want them to be signed, as they may
contain unvetted code.)
- Take advantage of the new -d option in buildvgl, which allows for
building from an existing Git clone directory.  This eliminates the need
to rename and restore .git/shallow, allows the official build scripts to
work properly when building PRs, and prevents 'git clone' being invoked
twice in CI builds.

Pixman: Revert compiler warning fix

Specific to pixman-access.c, 6d064a7
fixed some minor compiler warnings on one particular system, but it
introduced worse warnings on other systems.

Server: Fix div by 0 w/ zero-height PutImage reqs

These requests can be generated with XCB, since it does not perform the
same argument checking as Xlib.  Original commit message from X.org
appears below:

  From dc777c346d5d452a53b13b917c45f6a1bad2f20b Mon Sep 17 00:00:00 2001
  From: Keith Packard <keithp@keithp.com>
  Date: Sat, 3 Jan 2015 08:46:45 -0800
  Subject: [PATCH] dix: Allow zero-height PutImage requests

  The length checking code validates PutImage height and byte width by
  making sure that byte-width >= INT32_MAX / height. If height is zero,
  this generates a divide by zero exception. Allow zero height requests
  explicitly, bypassing the INT32_MAX check.

  Signed-off-by: Keith Packard <keithp@keithp.com>
  Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>

Java: Fix another NPE when dismissing Options dlg

<sigh> This is why we can't have nice things.

9d6a396 (exposing keyboarding grabbing
in the GUI) contained a logic error.  Because the || wasn't contained
within parantheses, the last condition-- which dereferenced viewport--
was evaluated even if viewport==null.  No bueno.

Fixes TurboVNC#49
Fixes TurboVNC#66

2.1 beta1

Doc: Bump revision to 2.0.2

ChangeLog.txt: Wordsmithing

Server: compiler warning