Instead, we use teh same binary we produce for the test case, and
add an extra switch -t that enables running the sequencer program.

This is so I can first start up the IOC, then switch to telnet console,
and then start the tests. The console output (quite verbose for some of
the tests) will be much faster in this way and the tests accordingly
more realistic.

- fixed a long-standing problem with parallel builds
- work-arounds for various EPICS base versions

William Steele reported and solved this.

This test was provided by Lewis Muir, it fails with seq-2.1.5.

This is now configurable in test/validate/Makefile.

This tests that for, while, if, and if/else statements
can be nested to at least depth 40.

Thanks to Mark Rivers who suggested this test.

As turned out, the 2.0.x branch supported this, so it is added
for compatibility.