Add --no-auto-insulate command-line flag

This flag disables automatic test insulation at the file level. When
this flag is enabled, all test insulation must be explicit, using the
`insulate` block. The file context will still wrap itself in a `setfenv`
sandbox, but the global tables `_G` and `package.loaded` will not be
saved/restored.

busted/modules/cli.lua

@@ -127,6 +127,7 @@ return function(options)
   cli:add_flag('-s, --enable-sound', 'executes `say` command if available', processOption)
   cli:add_flag('-l, --list', 'list the names of all tests instead of running them', processOption)
   cli:add_flag('--lazy', 'use lazy setup/teardown as the default', processOption)
+  cli:add_flag('--no-auto-insulate', 'disable file insulation', processOption)
   cli:add_flag('--no-keep-going', 'quit after first error or failure', processOption)
   cli:add_flag('--no-recursive', 'do not recurse into subdirectories', processOption)
   cli:add_flag('--shuffle', 'randomize file and test order, takes precedence over --sort (--shuffle-test and --shuffle-files)', processOption)

busted/runner.lua

@@ -55,6 +55,11 @@ return function(options)
     luacov()
   end
 
+  -- If auto-insulate is disabled, re-register file without insulation
+  if cliArgs['no-auto-insulate'] then
+    busted.register('file', 'file', {})
+  end
+
   -- If lazy is enabled, make lazy setup/teardown the default
   if cliArgs.lazy then
     busted.register('setup', 'lazy_setup')

completions/bash/busted.bash

@@ -155,6 +155,7 @@ _busted() {
       -Xoutput
       -Xhelper
       --lazy
+      --no-auto-insulate
       --no-keep-going
       --no-recursive
       --shuffle --shuffle-tests --shuffle-files

completions/zsh/_busted

@@ -20,6 +20,7 @@ _busted_args=(
 "--version[Prints the program version and exits]"
 "(-l --list)"{-l,--list}"[List the names of all tests instead of running them]"
 "--lazy[Use lazy setup/teardown as the default]"
+"--no-auto-insulate[Disable file insulation]"
 "--no-keep-going[Quit after first error or failure]"
 "--no-recursive[Do not recurse into subdirectories]"
 "--helper[A helper script that is run before tests]:files:_files"

spec/cl_spec.lua

@@ -734,6 +734,17 @@ describe('Tests no-recursive commandline option', function()
   end)
 end)
 
+describe('Tests no-auto-insulate commandline option', function()
+  it('does not insulate test files', function()
+    local success, exitcode
+    error_start()
+    success, exitcode = execute(busted_cmd .. ' --no-auto-insulate --pattern=insulate_file.*.lua$')
+    assert.is_false(success)
+    assert.is_equal(1, exitcode)
+    error_end()
+  end)
+end)
+
 describe('Tests Xoutput commandline option', function()
   it('forwards no options to output handler when no options specified', function()
     local result = run(busted_cmd .. ' --output=spec/cl_output_handler.lua --pattern=cl_success.lua$')