replace malloc+memcpy with strndup. no functional change intended ok stsp@

update client state tracking in the gotd parent process The session process takes over the old state definitions under a new name ("session state"). The parent only needs to keep track of whether a client has been granted access, so it only uses two states: NEW, and ACCCESS_GRANTED which is set as soon as the auth process has granted repository access and before the session and repo_read/repo_write children are started. Because 'gotctl info' can no longer observe the session state remove support code for printing it. ok op@

do not forget to initialize delta_cache_fd in the session process

add a gotd session process, split off from the parent process The new session process is able to manipulate files in the repository and keeps track of the read/write client session state. The parent process now restricts its view of the filesystem to the absolute path stored in argv[0], and combines this with unveil "x" on this path. As a result the parent process can only re-exec itself. small tweaks + ok op@