Workarounds and fixes for wrapped executables on various platforms
regarding the handling of wrapped dynamic libraries.

The basic flow of operation is to copy such libraries into a temp
file, hand them to the OS loader for processing, and then to delete
them immediately, to prevent them form being accessible to other
executables. On platforms where that is not possible the library is
left in place and things are arranged to delete it on regular process
exit.

An example of the latter are older revisions of HPUX which report that
the file is busy when trying to delete it. Younger revisions of HPUX
have changed to allow the deletion, but are also buggy, the OS loader
mangles its data structures so that a second library loaded in this
manner fails.

More recently it was found that Linux which is usually ok with
deleting the file and gets everything right shows the same trouble as
modern HPUX when the "docker" containerization system is involved, or
more specifically the AUFS in use there. Deleting the loaded library
file mangles data structures and breaks loading of the following
libraries. For a demonstration which does not involve Tcl at all see
the ticket

     https://github.com/dotcloud/docker/issues/1911

in the docker tracker.

This of course breaks the use of wrapped executables within docker
containers.

This commit introduces the function TclSkipUnlink() which centralizes
the handling of such exceptions to unlinking the library after unload,
and provides code handling the known cases. IOW HPUX is generally
forced to not unlink, and ditto when we detect that the copied library
file resides within an AUFS.

The latter must however be explicitly activated by setting the define
-DTCL_TEMPLOAD_NO_UNLINK during build. We still need proper configure
tests to set it on the relevant platforms (i.e. Linux).

The AUFS detection and handling can be overridden by the environment
variable TCL_TEMPLOAD_NO_UNLINK which can force the behaviour either
way (skip or not). In case the user knows best, or wishes to test if
the problem with AUFS has been fixed.
Followup on [72c54e1659]. Removed unused variable.
Comment out lines of test io-53.4 that appear to do nothing of any value.
Move code that can only matter in the first loop iteration out of the loop.
Increase size of test io-29.34 so that it more portably tests the case where
the OS networking machinery gets backed up and blocks.
Added several TODO comments on potential simplifications.
Expand the IsBufferFull() macro to check non-NULL bufPtr..
Further simplifications to FlushChannel().  This makes clear the
BUFFER_READY flag serves no necessary purpose, so it is removed.
Update comment to explain assumptions.
Refinements of FlushChannel() and its callers.  Notably includes removal
of the flag BUFFER_READY.
Merged the workarounds and fixes for wrapped executables on various
platforms into the trunk. For details see the merged revision and its
ancestor.
merge core-8-5-branch
Try not to loose FD_CONNECT by switching monitoring off.
Refinements of FlushChannel() and its callers. Notably includes removal of the flag BUFFER_READY.
win socket -async: do not loose connect notification by temporarily stop connect monitoring. Bug [336441ed59]
Correct the interest masks in the Tcl_CreateFileHandler() calls in
PipeWatchProc().  When we are interested in both readable and writable
events of a command pipeline channel, we only want the readable from
the read end of the pipe, and the writable from the write end of the pipe.
Correct the interest masks in the Tcl_CreateFileHandler() calls in PipeWatchProc(). When we are interested in both readable and writable events of a command pipeline channel, we only want the readable from the read end of the pipe, and the writable from the write end of the pipe.
Improve robustness of the socket tests against systems that support IPv6, but don't resolve localhost to ::1 (and vice versa for IPv4 and 127.0.0.1).
These edits make the tests socket-14.11.[01] stop hanging, but also introduce
a whole raft of test failures.  WIP.
These edits make all tests outside of socket-14.* pass on OSX Mavericks.
Several socket-14.* tests failing there, and those that pass are very slow
about it.  Firewall or poor networking configuration may be playing a role.
[1b0266d8bb] Working towards ensuring that all dict operations are sufficiently strict.