Allow optionally returning via a return from main, instead of calling

os.exit.

This ensures a saner teardown of the Lua state, which is mildly helpful
when instrumenting a run...
(e.g., there's a final GC cycle, among other things).

reader.lua

@@ -53,7 +53,9 @@ if G_reader_settings:isTrue("debug") and G_reader_settings:isTrue("debug_verbose
 -- Option parsing:
 local longopts = {
     debug = "d",
+    verbose = "d",
     profile = "p",
+    teardown = "t",
     help = "h",
 }
 
@@ -64,6 +66,7 @@ local function showusage()
     print("-d               start in debug mode")
     print("-v               debug in verbose mode")
     print("-p               enable Lua code profiling")
+    print("-t               teardown via a return instead of calling os.exit")
     print("-h               show this usage help")
     print("")
     print("If you give the name of a directory instead of a file path, a file")
@@ -76,6 +79,7 @@ local function showusage()
 end
 
 local Profiler = nil
+local sane_teardown
 local ARGV = arg
 local argidx = 1
 while argidx <= #ARGV do
@@ -97,6 +101,8 @@ while argidx <= #ARGV do
     elseif arg == "-p" then
         Profiler = require("jit.p")
         Profiler.start("la")
+    elseif arg == "-t" then
+        sane_teardown = true
     else
         -- not a recognized option, should be a filename
         argidx = argidx - 1
@@ -335,10 +341,20 @@ local function exitReader()
     if Profiler then Profiler.stop() end
 
     if type(exit_code) == "number" then
-        os.exit(exit_code)
+        return exit_code
     else
-        os.exit(0)
+        return 0
     end
 end
 
-exitReader()
+local ret = exitReader()
+
+if not sane_teardown then
+    os.exit(ret)
+else
+    -- NOTE: We can unfortunately not return with a custom exit code...
+    --       But since this should only really be used on the emulator,
+    --       to ensure a saner teardown of ressources when debugging,
+    --       it's not a great loss...
+    return
+end