doc/go1.4: add note about Set{uid,gid} change

LGTM=iant
R=ruiu, iant
CC=golang-codereviews
https://golang.org/cl/107320044

doc/go1.4.txt

@@ -6,4 +6,5 @@ package or cmd/xxx directory name, and ending in a CL number.
 Please keep the list sorted (as in sort.Strings of the lines).
 
 runtime/race: freebsd is supported (CL 107270043)
+syscall: Setuid, Setgid are disabled on linux platforms. On linux those syscalls operate on the calling thread, not the whole process. This does not match the semantics of other platforms, nor the expectations of the caller, so the operations have been disabled until issue 1435 is resolved (CL 106170043)
 time: use the micro symbol (µ (U+00B5)) to print microsecond duration (CL 105030046)