* dcrt0.cc (dll_crt0_1): init cygcwd before forkee branch

* dcrt0.cc (dll_crt0_1): init cygcwd before forkee branch

* environ.cc (conv_start_chars): Cache a table of "first
characters" for environment variables needing conversion.
(getwinenv): Use it.
(environ_init): Create it, also check first chars for TERM and
CYGWIN.

* path.cc: Use lookup table for case insensitive comparisons.