build failure on hp-ux due to incorrect shlib link opt, suffix

[Michael Pelletier]

The HP-UX 11.11 operating system requires shared libraries to have a ".sl" suffix, whereas the Makefile uses ".so" throughout. Creating a symbolic link to the .so file works, though may not be the most desirable solution. I simply made updates to the Makefile to create the symlink during both build and install.

In addition, the linker option to build a shared library is incorrect in the "else" clause of the "SunOS" check. It needs to be "+b" to support the HP-UX 11.11 linker, which doesn't recognize the "-soname" option:

 $(CC) $(CFLAGS) -shared -Wl,+b,libtokyocabinet.so.$(LIBVER) -o $@ \

I added another "if" to check for uname -a | grep "HP-UX"