RFC: Change pwd to assume -L by default

[Pádraig Brady]

POSIX says that `pwd` without options should assume -L is specified.
pwd is most often invoked as a shell builtin and bash, dash, zsh, ksh
all follow POSIX and assume that -L is the default.
However coreutils pwd assumes -P is the default, according to this
comment in the source:

  "POSIX requires a default of -L, but most scripts expect -P."

I'm not sure that is correct though, since the vast majority
of scripts would be executing the shell builtin?

Note also that the solaris sh builtin and separate pwd util
only support -P behavior.

thanks,
Pádraig.