More work on OS X launcher.

Change-Id: Id88e5f1c26b536b4a296f25b08bb4375ea014dc5
Merge "More work on OS X launcher."
Document environment variables usage.

Running 'go run dev/envvardoc/envvardoc.go' now shows:
'All environment variables are documented'

I also took the liberty of cleaning-up our mishmash of logic for handling
boolean environment variables, and cleaned up a couple other spots that didn't
seem right.

This change adds docmentation for all variables starting with (CAM|DEV|AWS).
This leaves some variables still undocumented.  If there are variables worth
documenting in the following list, maybe we should rename them to have a
CAM{LI} prefix for consistency's sake:

APPDATA                  pkg/osutil/paths.go:86
APPDATA                  pkg/osutil/paths.go:102
DISPLAY                  pkg/misc/gpgagent/gpgagent.go:126
GOPATH                   pkg/fileembed/genfileembed/genfileembed.go:321
GOPATH                   pkg/osutil/paths.go:168
GOPATH                   pkg/test/world.go:54
GOPATH                   server/appengine/build_test.go:77
GPGKEY                   cmd/camput/init.go:77
GPG_AGENT_INFO           cmd/camput/init.go:153
GPG_AGENT_INFO           pkg/misc/gpgagent/gpgagent.go:50
HOME                     pkg/jsonsign/keys.go:79
HOME                     pkg/jsonsign/signhandler/sig.go:64
HOME                     pkg/osutil/paths.go:36
HOMEPATH                 pkg/osutil/paths.go:34
PKG_CONFIG_PATH          pkg/index/sqlite/dbschema.go:59
RUN_BROKEN_TESTS         pkg/fs/fs_test.go:67
SKIP_DEP_TESTS           pkg/test/testdep.go:29
TERM                     pkg/misc/gpgagent/gpgagent.go:133
TERM                     pkg/misc/pinentry/pinentry.go:99
TESTING_PORT_WRITE_FD    pkg/webserver/webserver.go:135
TEST_GPGAGENT_LIB        pkg/misc/gpgagent/gpgagent_test.go:27
USER                     pkg/netutil/ident.go:135
USER                     pkg/osutil/paths.go:45
USERNAME                 pkg/jsonconfig/eval.go:228
USERNAME                 pkg/osutil/paths.go:43
VERBOSE_FUSE             pkg/fs/fs_test.go:133
VERBOSE_FUSE_STDERR      pkg/fs/fs_test.go:137
XDG_CONFIG_HOME          pkg/osutil/paths.go:104

Change-Id: Ief28710d3deefd1e65247cb5d3b1d8dde73e1f2d
Fix crash in `camput file` when configuration discovery has failed.

Change-Id: I8a7ac26e5d550f25eddf149dadde5013a1d50fe7
Merge "Document environment variables usage."
devcam: fix breakage caused from envvar strconv changes.

Change-Id: Id05d00d9b82924242905ccbc7a7e8002dc4859a7