Normally one would dlopen() a shared object's basename, not its absolute
path. However, lib/krb5/plugin.c, in an effort to be zero-conf-ish,
wants to readdir() to find plugins to load, and in the process it ends
up defeating the RTLD's search-the-caller's-rpath.
This commit partially addresses this by allowing the use of $ORIGIN in
plugin_dir values and using them for the default (except on OS X).
This allows multiple Heimdal versions installed on the same host, but
with different plugin ABIs, to co-exist. A step forward for doing make
check on hosts where Heimdal is installed.
For now we hardcode $ORIGIN/../lib/plugin/krb5 (linux, Solaris, *BSD),
or $ORIGIN (Windows; for assemblies objects need to be in the same
directory) and we eval $ORIGIN by using dladdr() (Linux, Solaris) or
GetModuleHandleEx() (Win32, via a dladdr() wrapper in libroken) to find
the path to libkrb5 whose dirname to use as $ORIGIN. For Windows,
because we need the plugins to be in the same directory as libkrb5, we
require a prefix on plugin DLLs ("plugin_krb5_") to distinguish them
from other objects.
We should add a special token to mean "look in $ORIGIN, sure, but
dlopen() the plugin basenames only (so the RTLD can search the rpath)".
A colon can't be used to separate paths on Windows since they are used
in drive sepecification. Define a macro that can be used as a path
separator string. On Windows, this is defined as ";". It is a ":"
everywhere else.
HAVE_WINDNS is defined when we want to use DNSAPI on Windows which
handles most of the resolver work for us.
NO_LIMIT_FD_SETSIZE is defined if the value of a socket FD does not
imply anything about the number of sockets so far assigned.
I.e. checking if the socket is larger than FD_SETSIZE is incorrect.
