Ensure no autoinit loop when set_shell_startup set

Set the __MODULES_AUTOINIT_INPROGRESS environment variable when running
the `autoinit` sub-command and quit autoinit process if this variable is
found defined and equal to 1 when starting it. Ensure this way that an
autoinit process will not be triggered indefinitely by itself when the
set_shell_startup option is enabled and some module loaded at
initialization time relies on the execution of a bash script.

Fixes #414.

Author: xdelaruelle

tcl/subcmd.tcl.in

@@ -1668,6 +1668,14 @@ proc cmdModuleUnuse {args} {
 proc cmdModuleAutoinit {} {
    reportDebug called.
 
+   # skip autoinit process if found already ongoing in current environment
+   if {[get-env __MODULES_AUTOINIT_INPROGRESS] eq {1}} {
+      return
+   }
+
+   # set environment variable to state autoinit process is ongoing
+   setenv __MODULES_AUTOINIT_INPROGRESS 1
+
    # flag to make renderSettings define the module command
    setState autoinit 1
 
@@ -1751,6 +1759,9 @@ proc cmdModuleAutoinit {} {
       setenv BASH_ENV @initdir@/bash
    }
 
+   # clear in progress flag
+   unsetenv __MODULES_AUTOINIT_INPROGRESS
+
    lpopState mode
 }