SBCL compiler notes should not be fatal to pgloader.

[dimitri]

The compile function returns warnings-p and failure-p values, use that to decide if the code could be compiled, and only signal a condition when it has been fatal to compiling the code at run-time.

The SBCL compiler is getting smarter at removing unreachable code, and it looks like pgloader is producing some unreachable code from parsing the user provided commands.

Fixes #1407