[Factor-builds] mason on linux-x86-64: build loop error

[<fac...@gm...>]

Fatal error on arch-mason

Unix system call “mkdir” failed:

File exists (17)

It was called with the following arguments:

"/home/sheeple/builds/2014-11-08-08-48"
511
(U) Quotation: [ set-namestack init-catchstack self quot>> call -> stop ]
(O) Word: build-loop
(O) Word: build
(O) Method: M\ unix make-directory
(O) Word: unix-system-call-error
(O) Method: M\ object throw
(U) Quotation: [
        OBJ-CURRENT-THREAD special-object error-thread set-global
        current-continuation -> error-continuation set-global
        [ original-error set-global ] [ rethrow ] bi
    ]