eLua stack overflow fix

DETAILS: for most platforms, the main stack size was set to 256 bytes to
save RAM. During a routine Lua debugging session, I discovered that there
are at least two data structures in Lua (declared on the stack) that can
lead to a stack overflow problem because of their size:

lparser.h -> struct FuncState (original size: 572) is allocated on the stack
when the parser needs to compile a Lua function
lstrlib.c -> MatchState (original size: 272) is allocated on the stack
everytime the string library does match-related operations.

To fix the first problem I modified these macros in luaconf.h:

/*
@@ LUAI_MAXUPVALUES is the maximum number of upvalues per function
@* (must be smaller than 250).
*/

LUAI_MAXUPVALUES from 60 to 10

/*
@@ LUAI_MAXVARS is the maximum number of local variables per function
@* (must be smaller than 250).
*/
LUAI_MAXVARS from 200 to 25

The new size of the FuncState structure: 124

To fix the second problem I modified this macro in luaconf.g

/*
@@ LUA_MAXCAPTURES is the maximum number of captures that a pattern
@* can do during pattern-matching.
** CHANGE it if you need more captures. This limit is arbitrary.
*/

LUA_MAXCAPTURES from 32 to 10

The new size of the MatchState structure: 96

All these values are experimental, but they should work well.

Also, I forced the main stack to 512 bytes in all the backends. Hopefully
this will take care of this problem.

src/lua/luaconf.h

@@ -486,14 +486,14 @@
 @@ LUAI_MAXVARS is the maximum number of local variables per function
 @* (must be smaller than 250).
 */
-#define LUAI_MAXVARS		200
+#define LUAI_MAXVARS		25
 
 
 /*
 @@ LUAI_MAXUPVALUES is the maximum number of upvalues per function
 @* (must be smaller than 250).
 */
-#define LUAI_MAXUPVALUES	60
+#define LUAI_MAXUPVALUES	10
 
 
 /*
@@ -696,7 +696,7 @@ union luai_Cast { double l_d; long l_l; };
 @* can do during pattern-matching.
 ** CHANGE it if you need more captures. This limit is arbitrary.
 */
-#define LUA_MAXCAPTURES		32
+#define LUA_MAXCAPTURES		10
 
 
 /*

src/platform/at91sam7x/stacks.h

@@ -3,7 +3,7 @@
 #ifndef __STACKS_H__
 #define __STACKS_H__
 
-#define  STACK_SIZE_USR   256
+#define  STACK_SIZE_USR   512
 #define  STACK_SIZE_IRQ   64
 #define  STACK_SIZE_TOTAL ( STACK_SIZE_USR + STACK_SIZE_IRQ )
 

src/platform/lpc288x/stacks.h

@@ -3,7 +3,7 @@
 #ifndef __STACKS_H__
 #define __STACKS_H__
 
-#define STACK_SIZE_SVC   256
+#define STACK_SIZE_SVC   512
 #define STACK_SIZE_IRQ   32
 #define STACK_SIZE_TOTAL ( STACK_SIZE_SVC + STACK_SIZE_IRQ )
 

src/platform/str7/stacks.h

@@ -3,7 +3,7 @@
 #ifndef __STACKS_H__
 #define __STACKS_H__
 
-#define  STACK_SIZE_USR   256
+#define  STACK_SIZE_USR   512
 #define  STACK_SIZE_TOTAL ( STACK_SIZE_USR )
 
 #endif

src/platform/str9/stacks.h

@@ -3,9 +3,8 @@
 #ifndef __STACKS_H__
 #define __STACKS_H__
 
-#define STACK_SIZE_USR   256
-#define STACK_SIZE_SVC   32
+#define STACK_SIZE_SVC   512
 #define STACK_SIZE_IRQ   32
-#define STACK_SIZE_TOTAL ( STACK_SIZE_USR + STACK_SIZE_SVC + STACK_SIZE_IRQ )
+#define STACK_SIZE_TOTAL ( STACK_SIZE_SVC + STACK_SIZE_IRQ )
 
 #endif

src/platform/str9/startup912.s

@@ -251,13 +251,8 @@ PLL_LOCK_LOOP:
               sub     r0, r0, #STACK_SIZE_IRQ                  
 
 #    Set up Supervisor Mode and set Supervisor Mode Stack
-              msr     CPSR_c, #Mode_SVC|I_BIT|F_BIT
+              msr     CPSR_c, #Mode_SVC
               mov     r13, r0
-              sub     r0, r0, #STACK_SIZE_SVC
-
-#    Set up User Mode and set User Mode Stack
-              msr     CPSR_c, #Mode_USR   /* Leave interrupts enabled in user mode                 */
-              mov     r13, r0             /* Note: interrupts will not happen until VIC is enabled */
 
 #*************************************************************************
 # Initialise RAM For Compiler Variables