Hello all,

Here's a preliminary patch to avoid modifying LD_LIBRARY_PATH.

Following Bruce's suggestion, it causes 'sysdep_dynl_link' to manually
search additional directories if 'lt_dlopenext' fails to find the
library in the default paths.  However, I took a somewhat different
approach, and tried to be more careful with regard to portability and
correctness.

I read the code of libltdl, and mimicked their handling of path
separators and directory separators, to ensure that this patch will not
reduce our portability.

I also followed their lead in deciding when to perform a search.  If any
directory separators are present (even if it's a relative pathname),
then libltdl does not perform a search.  I used precisely the same
criterion to decide whether to search additional directories.

So what additional directories does it search?

If GUILE_SYSTEM_EXTENSIONS_PATH is set (even if it's empty), then it
specifies the additional directories to search.  If it's unset, then the
default is to search SCM_LIB_DIR and SCM_EXTENSIONS_DIR.

*** Note that this changes the search order in the case where
GUILE_SYSTEM_EXTENSIONS_PATH is set to a non-empty string.

Currently, a non-empty GUILE_SYSTEM_EXTENSIONS_PATH is passed to
lt_dladdsearchdir, so it is searched before LTDL_LIBRARY_PATH and
LD_LIBRARY_PATH, but this patch causes GUILE_SYSTEM_EXTENSIONS_PATH to
be searched last, to be consistent with the handling of the default
directories SCM_LIB_DIR and SCM_EXTENSIONS_DIR.  This seems sensible to
me.  Does anyone see a problem with this change?

This patch also adds robust handling of the case where
GUILE_SYSTEM_EXTENSIONS_PATH contains more than one path component.

See below for my preliminary patch.  I have not yet tested it carefully.
It's a context diff, because 'diff' made a mess of the unified diff.

Comments and suggestions solicited.

     Mark