[gentoo-user] libjpeg, 6 vs 7, and emacs

Gentoo updates refuse to install both versions 6 and 7 of jpeg,
and I have found that certain applications, like emacs, refuse
to remerge with -7 so I have been refusing the -7 update for a
month or two now.  Every once in a while, one slips by me,
usually because I forget to remove thunderbird from the list of
updates, and I find out when emacs won't run.  If I try to build
emacs with -7, it complains, so I remerge jpeg-6 and then emacs
is happy again.  I do not understand the compat lib; it also blocks,
and since I can just refuse the -7 update and keep on working, I
have not looked into it much, figuring that sooner or later emacs
and other packages will be upgraded to handle jpeg-7.

Recently another jpeg-7 upgrade slipped past me, only this time it
got weird.  I remerged jpeg-6 and found that emacs now complained
that jpeg-7 was missing.  Here is "ldd /usr/emacs/bin|grep jpeg":

	libjpeg.so.62 => /usr/lib/libjpeg.so.62 (0x00007f0cbd19f000)
	libjpeg.so.7 => not found

Now I am puzzled.   If jpeg-6 and -7 block each other, how did
emacs end up expecting both?  If I try to emerge emacs with -6
installed and -7 missing, it complains that gtk is not installed properly.

Obviously I am doing something wrong.  Gentoo documentation on the
jpeg compatibility lib is so minimal as to be useless, unless I
have just not found the right documentation.  If that is the right
solution to my mess, I'd like to get it working, but I can't figure
out how to emerge the compatibility library when it blocks.

These are the packages that would be merged, in order:

Calculating dependencies  .... done!
[ebuild  N    ] media-libs/jpeg-compat-6b-r1  0 kB
[blocks B     ] <media-libs/jpeg-7 ("<media-libs/jpeg-7" is blocking media-libs/jpeg-compat-6b-r1)

Total: 1 package (1 new), Size of downloads: 0 kB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  ('ebuild', '/', 'media-libs/jpeg-compat-6b-r1', 'merge') pulled in by
    media-libs/jpeg-compat

  ('installed', '/', 'media-libs/jpeg-6b-r8', 'nomerge') pulled in by
    media-libs/jpeg required by ('installed', '/', 'x11-libs/qt-3.3.8b-r2', 'nomerge')
    media-libs/jpeg required by ('installed', '/', 'x11-libs/openmotif-2.3.2', 'nomerge')
    media-libs/jpeg required by ('installed', '/', 'dev-python/wxpython-2.6.4.0-r2', 'nomerge')
    (and 88 more)

-- 
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     Felix Finch: scarecrow repairman & rocket surgeon / felix@×××××××.com
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I've found a solution to Fermat's Last Theorem but I see I've run out of room o