fixup shebang - build was not running fixupPhase, and shebang was pointing to
/bin/sh. On a system where /bin/sh links to dash, this results in errors:
/nix/store/v40yk16fl1rhvr6zz91ij753ziyphwwp-keychain-2.8.0/bin/.keychain-wrapped: 59: /nix/store/v40yk16fl1rhvr6zz91ij753ziyphwwp-keychain-2.8.0/bin/.keychain-wrapped: shopt: not found
/nix/store/v40yk16fl1rhvr6zz91ij753ziyphwwp-keychain-2.8.0/bin/.keychain-wrapped: 686: /nix/store/v40yk16fl1rhvr6zz91ij753ziyphwwp-keychain-2.8.0/bin/.keychain-wrapped: Syntax error: "(" unexpected (expecting ")")
use upstream builder - the include Makefile uses perl to generate a manpage and
insert the same text into the keychain script for '--help' output, which was
otherwise missing:
$ keychain --help
* keychain 2.8.0 ~ http://www.funtoo.org
[snip]
INSERT_POD_OUTPUT_HERE
install manpage - self explanatory
