Option for specifying forkserver initialization timeout via environment variable (#522)

* Addition of AFL_FORKSRV_INIT_TMOUT env var

This commit introduces a new environment variable which allows to
specify the timespan AFL should wait for initial contact with the
forkserver.

This is useful for fuzz-targets requiring a rather long setup time
before the actual fuzzing can be started (e.g., unicorn).

* add .swp files to .gitignore

* Inherit init_tmout in afl_fsrv_init_dup

Without this patch, the forkserver would spawn with a timeout of 0 in
cmplog mode, leading to an immediate crash.

Additionally, this commit removes a spurious whitespace.

* Initialize afl->fsrv.init_tmout in afl_fsrv_init

Not all afl-components will need the new AFL_FORKSRV_INIT_TMOUT
environment variable. Hence, it's initialized to the safe "default"
value from before in afl_fsrv_init now.

src/afl-fuzz-state.c

@@ -356,6 +356,13 @@ void read_afl_environment(afl_state_t *afl, char **envp) {
             afl->afl_env.afl_max_det_extras =
                 (u8 *)get_afl_env(afl_environment_variables[i]);
 
+          } else if (!strncmp(env, "AFL_FORKSRV_INIT_TMOUT",
+
+                              afl_environment_variable_len)) {
+
+            afl->afl_env.afl_forksrv_init_tmout =
+                (u8 *) get_afl_env(afl_environment_variables[i]);
+
           }
 
         } else {