Use isfinite() instead of finite() when available

OS X Mavericks builds result in a number of warnings about finite() being
deprecated, like these:

beam/erl_arith.c:451:7: warning: 'finite' is deprecated: first deprecated in OS X 10.9 [-Wdeprecated-declarations]
                    ERTS_FP_ERROR(p, f1.fd, goto badarith);
                    ^
sys/unix/erl_unix_sys.h:319:33: note: expanded from macro 'ERTS_FP_ERROR'
                                        ^
sys/unix/erl_unix_sys.h:244:51: note: expanded from macro '__ERTS_FP_ERROR'
                                                  ^
/usr/include/math.h:718:12: note: 'finite' has been explicitly marked deprecated here
extern int finite(double) __OSX_AVAILABLE_BUT_DEPRECATED(__MAC_10_0, __MAC_10_9, __IPHONE_NA, __IPHONE_NA);

Add checks to use isfinite() instead of finite() where available. Verified
on OS X Mavericks 10.9.5 and Ubuntu 12.04.