MAINT: fix up use of NPY_NO_DEPRECATED_API usage in f2py

This was giving a lot of warnings like:

    numpy/f2py/src/fortranobject.h:9: warning: "NPY_NO_DEPRECATED_API" redefined

when building SciPy. In general, this is generated code which is
included in the build of other projects which may have already set this
macro - so only set it if it is not yet set.

The other change is to set it to the current numpy version, like is done
everywhere else in numpy, rather than to a fixed 1.7 version.
This will ensure that if new deprecations happen, f2py gets updated for
them.

numpy/f2py/src/fortranobject.h

@@ -6,7 +6,9 @@ extern "C" {
 
 #include <Python.h>
 
-#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
+#ifndef NPY_NO_DEPRECATED_API
+#define NPY_NO_DEPRECATED_API NPY_API_VERSION
+#endif
 #ifdef FORTRANOBJECT_C
 #define NO_IMPORT_ARRAY
 #endif