Separate SH used to run Configure from SH used on target system

This is because, for example, on the host system, sh might be /bin/sh,
but on the target system, it's /system/bin/sh.

The new variable is "targetsh" and defaults to "sh" unless changed by the hints file/Configure params.
Added targetsh to all the canned config files
Glossary entry for targetsh
regen for uconfig.h
perldelta for -Dtargetsh