gitk: switch to -translation binary

gitk uses '-encoding binary' in several places to handle non-text data.
Per TIP 699, this is not recommended as there has been too much
confusion and misconfiguration of binary channels, and this option is
removed in Tcl 9.

Tcl defines a binary channel as one that reproduces the input data
exactly. As Tcl stores all data internally in unicode format, a binary
channel requires 3 things:
-  -encoding iso8859-1 : this causes each byte of input to be translated
   to its unicode equivalent (may be multi-byte).
-  -translation lf : this avoids any translation of line endings, which
   by default are translated to \n on input.
-  -eofchar {} : this avoids any use of an end of file character, which
   is ctrl-z by default on Windows.

The recommended '-translation binary' makes all three settings, but this
is not done in gitk now. Rather, gitk uses '-encoding binary', which is
an alias to '-encoding iso8859-1' removed by TIP 699, in multiple places,
and -eofchar {} in one place but not all. All other files, configured in
non-binary fashion, have -eofchar {}.

Unix and Windows differ on line ending conventions, Tcl by default
converts line endings to \n on input, and to those common on the
platform on output. git emits only \n on Unix or Windows. Also, Tcl's
proc gets recognizes and removes \n, \r, or \r\n as line endings, and
this is used by gitk except in procs selectline and parsecommit. But,
those two procs recognize any combination of \n and \r as terminating a
line. So, there is no need to translate line endings on input, and using
-translation binary avoids any such translation.

Tcl sets eofchar to ctrl-z (ascii \0x1a) only on Windows, otherwise
eofchar is {}. This provides compatibility to old DOS based codes and
files originating when file systems recorded only sectors allocated, and
not bytes used. git does not use ctrl-z to terminate data anywhere. Only
two channels in gitk leave eofchar at the default value, both use
-encoding binary now. A third one was converted in commit 681c3290e3
("gitk: Handle blobs containing a DOS end-of-file marker", 2009-03-16),
fixing such a problem of early data termination. Using eofchar {} is
correct, even if not always necessary.

Tcl 9 forces change, using -translation binary per TIP 699 does what
gitk needs and is backwards compatible to Tcl 8.x. Do it.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>

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