Add a f2py_path option to the scons script.

Sometimes the virtualenv version of f2py does not take precedence over
the system-wide one if any. It is now possible to enforce a given
f2py path.

src/SConstruct

@@ -1,4 +1,5 @@
 import os
+import subprocess
 
 ###############################################################################
 def filtered_glob(env, pattern, omit=[],
@@ -16,7 +17,8 @@ def f2py_generator(source, target, env, for_signature):
     modulefile = str(target[0])
     modulename = modulefile.replace(suffix, '').replace('/', '.')
     compiler = env['FORTRAN']
-    cmd  = f"f2py3 --fcompiler={compiler} "
+    
+    cmd  = f"$F2PY --fcompiler={compiler} "
     cmd += f" $F2PY_OPTS -m {modulename} -c {objects} {main}"
     cmd += f" && cp {'/'.join(modulename.split('.'))}.*.so {modulefile}"
     #cmd += " 1>/dev/null 2>/dev/null"
@@ -55,6 +57,10 @@ AddOption('--compiler',
           choices=['gfortran', 'ifort'],
           help='The Fortran compiler to use')
 
+AddOption('--f2py_path',
+          dest='f2py_path',
+          default='f2py3',
+          help='The full path to the f2py compiler')
 
 
 
@@ -71,6 +77,13 @@ if GetOption('compiler') == 'gfortran':
 elif GetOption('compiler') == 'ifort':
 	env = ifort_env
 
+f2py_path = GetOption('f2py_path')
+p = subprocess.run(['which', f2py_path], stdout=subprocess.PIPE)
+if p.returncode != 0:
+    raise Exception('Invalid path for f2py compiler!')
+else:
+    env.Append(F2PY=p.stdout.decode('utf8').strip())
+
 if GetOption('dbg'):
     gfortran_env.Append(FORTRANFLAGS = ['-g', '-Wall', '-Wextra', '-Warray-temporaries', 
                                         '-Wconversion', '-fbacktrace', '-ffree-line-length-0',