Additions for OS X

[Per Persson]

Hi,
I've been adding a few pieces to get octave building out-of-the box for 
OS X.
In particular I'd like your opinion on the way I'm thinking about 
handling errors in BLAS routines.
Presently this is done by providing our own implementation of xerbla, 
but the Mach-O format of OS X does not allow this kind of approach.
The BLAS libs provided in OS X allows us to install an error handler 
instead, so I introduced a INSTALL_BLAS_ERRORHANDLER option in 
configure which leaves XERBLA to be empty in src/Makefile if true (see 
below). This flag would also be used to actually switch in error 
handling code. Is this an acceptable change?

/Per

ifeq ($(INSTALL_BLAS_ERRORHANDLER), true)
  TMP_XERBLA =
  TMP_XERBLAPIC =
else
  TMP_XERBLA = ../libcruft/blas-xtra/xerbla.o
  TMP_XERBLAPIC = ../libcruft/blas-xtra/pic/xerbla.o
endif

XERBLA = $(TMP_XERBLA)

ifeq ($(SHARED_LIBS), true)
  ifeq ($(STATIC_LIBS), true)
    LIBRARIES = liboctinterp.$(LIBEXT) liboctinterp.$(SHLEXT_VER)  else
    LIBRARIES = liboctinterp.$(SHLEXT_VER)
    ifdef FPICFLAG
      XERBLA = $(TMP_XERBLAPIC)
    endif
  endif
else
  ifeq ($(STATIC_LIBS), true)
    LIBRARIES = liboctinterp.$(LIBEXT)
  else
    ## This is not going to work, but hey, you asked for it...
    LIBRARIES =
    XERBLA =
  endif
endif