BUG: Choose a more unique PY_ARRAY_UNIQUE_SYMBOL in f2py.

In a few exceptional cases where symbols are shared between different Python
modules the use of `PyArray_API` in f2py (fortranobject.h) conflicts with the
regular use of the same symbol in the multiarray module. Generally the symptom
of this conflicting use is a segfault when importing a f2py'ed module. This
occurs because the module init code somehow overwrites the first element of
`PyArray_API` with the location of `PyArray_API`, causing a crash when
`PyArray_GetNDArrayCVersion` is called.

Closes gh-2521.