Solaris compatibility

Fix md5.c++ to work on non x86 systems

ctx is not a pointer but was being used with the arrow operator on non-x86 systems

Fix LDFLAGS and work around a Fedora bug that broke pthread linking

The Fedora bug caused the DT_NEEDED for libpthread to be omitted, and
the missing -Wl before no-undefined prevented binutils from detecting it.

-export-dynamic is unnecessary for libraries, so this removes it, too.

Improve test scripts, and add a new mega-test script which runs super-test on all platforms in parallel with progress bars.

Fix bug where only the first import made it into the import table.  Can't believe this wasn't tested.  Sigh.

Make sure generated code compiles cleanly even with pedantic warnings, since some people enable those.

Don't delete default dynamic builder constructors, because this makes things difficult for the Python wrappers.

Fix linking problems that only come up when using Ubuntu's libtool to build a dist and then installing it on OSX.  libkj.la was not listed in libcapnpc's deps.  Also put the pthread libs last since that's more correct.