[Bug-apl] r819 has severe performance issue

[David B. Lamkins]

Revision 819 causes *severe* performance issues for my APL Packager.

https://github.com/TieDyedDevil/apl-pkg
(Use the `percy` branch.)

$ git clone https://github.com/TieDyedDevil/apl-pkg
# cd apl-pkg
$ git branch percy
$ ./install.sh
$ awe

Normally the system comes up in a second or so; under r819 it takes tens of 
minutes to complete, during which one CPU core is pegged. (It's slow enough 
that I first thought that some altered edge condition must've caused an 
infinite loop.)

Memory usage is stable.

FWIW, this happens in the packager's boot loader, so there's not a lot of APL 
code involved.

https://github.com/TieDyedDevil/apl-pkg/blob/percy/boot/gnu-apl-linux.apl

Once past the boot loader (which took about 90 minutes on my Haswell i7 
notebook), virtually every packager operation is noticeably slow. If I had to 
guess, I'd suspect that either branching or APL function calls are eating a lot 
of cycles unnecessarily; my code uses lots of both.