dll installation logic

[Robert Collins]

The current cygwin shared library installation logic seems to be

"install path"../bin

This fails for things like l3 in depdemo where the install dir is

extradir = $(libdir)/extra
extra_LTLIBRARIES = libl3.la

I'm not sure what we should use as install logic... maybe walk up the
install path until we reach a 'lib' dir and then apply the ../bin rule.
The problem being that libtool linked .exe's won't find the needed .dll
unless the directory is in the dll search path. Add to this that the
first found .dll is always used.. and installing every dll into either
/usr/bin or /usr/local/bin almost makes sense.

Thoughts?
(This is the failure reason for depdemo-exec when depdemo has been built
with shared librarys).

Rob