only LOG() the DPI when it changes, DLOG() it otherwise (Thanks lkraav)

This avoids flooding stdout every time some text (e.g. a window
decoration) is drawn, yet leaves the message in place when it’s actually
relevant (upon DPI changes).

fixes #1115
Merge branch 'dpi-log'
i3bar: Set `mapped` flag on trayclient creation

When a trayclient is first created as a structure in memory, explicitly
set the `mapped` flag to false. Otherwise it may initialize to `true` in
some circumstances without actually being mapped, causing a request to
be mapped from the client to be ignored.

Create the trayclient in memory before handling a request to be mapped
immediately.

fixes #1138
Merge branch 'fix-tray-mapped'
docs/debugging: use bzip2 for consistency with the new ticket form (Thanks x33a)
docs/debugging: update version numbers
docs/debugging: explain how to enable logging on the fly
docs/debugging: include supported version, recommend --moreversion
docs/debugging: merge the debug symbols/backtrace section

We rarely have crashes, almost always we just need logs.
docs/debugging: use a version command that will work with i3 < 4.3
enable shmlog when invoked as i3-with-shmlog, install symlink + .desktop file
Merge branch 'docs-debugging'
install i3-with-shmlog.xsession.desktop, overwrite symlink if it exists
Merge branch 'docs-debugging'