devel/pstreams: 0.8.0 -> 0.8.1

• pstream.h (basic_ipstream::basic_ipstream(argv_type, pmode): o Use basic_ipstream::readable(pmode) to correctly set input mode. o Add initializer-list constructors. o Make unary constructors explicit.
• test_pstreams.cc: o Test execve-style construction for ipstream.

PR: 206272
Submitted by: yuri@rawbw.com
Approved by: eg@fbsd.lt (maintainer timeout)