* boot-9.scm (error): replace another throw with scm-error. Throw

* boot-9.scm (error): replace another throw with scm-error.  Throw
to 'misc-error instead of 'error (no need to distinguish these.)
Don't set up 'error as a key.
Set up regex-error as a key, if regex is available.
(signal-handler): use scm-error, not throw.

(%try-load, try-load-with-path, %load, load-with-path,
basic-try-load-with-path, basic-load-with-path,
try-load-module-with-path,load-module-with-path): deleted, since
they seem redundant.
(try-load): define using %try-load, not try-load-with-path.
(load): rewritten.  load tries to open the file directly and
with a .scm extension before searching the library directories
(should "." be added to %load-path?  then load could still open
directly files starting with "/").
(try-module-autoload): use load, not load-with-path.
(%load-indent): deleted, -2 was causing errors.

(%read-sharp): use port-line, not line-number.