tests: Split out those tests requiring float and import.

Tests in basics (which should probably be renamed to core) should not
rely on float, or import any non-built-in files.  This way these tests
can be run when those features are not available.

All test in basics now pass on the pyboard using stmhal port, except for
string-repr which has some issues with character hex printing.

tests/import/try-module.py

@@ -0,0 +1,15 @@
+# Regression test for #290 - throwing exception in another module led to
+# its namespace stick and namespace of current module not coming back.
+import import1b
+
+def func1():
+    print('func1')
+
+def func2():
+    try:
+        import1b.throw()
+    except ValueError:
+        pass
+    func1()
+
+func2()