[rb-general] BUILD_PATH_PREFIX_MAP code examples and test cases

[Ian Jackson]

Ximin Luo writes ("[rb-general] BUILD_PATH_PREFIX_MAP code examples and test cases"):
> I made some minor changes on top of the proposal from last time; the mapping is now:
> 
> % -> %p
> = -> %e
> : -> %c

Please don't use letters (or underscore, or ideally, hyphens) for
this.  There are all sorts of informal and semi-formal string handling
algorithms that depend on finding the boundaries of `words' consisting
of alphanumerics.  They will not work right, generating an endless
stream of low-level lossage for human expert users writing ad-hoc
regexps, doing cut and paste, and so on.

These approaches can also mislead wetware and sometimes cause false
matches in software.  (These problem are evident in QP- and
URL-encodings.)

Ian.