Concat object is based on "luaL_Buffer". The luaL_Buffer documentation says:
During its normal operation, a string buffer uses a variable number of stack
slots. So, while using a buffer, you cannot assume that you know where the
top of the stack is. You can use the stack between successive calls to buffer
operations as long as that use is balanced; that is, when you call a buffer
operation, the stack is at the same level it was immediately after the
previous buffer operation. (The only exception to this rule is
luaL_addvalue.) After calling luaL_pushresult the stack is back to its level
when the buffer was initialized, plus the final string on its top.
So, the stack cannot be manipulated between the first call at the function
"luaL_buffinit()" and the last call to the function "luaL_pushresult()" because
we cannot known the stack status.
In other way, the memory used by these functions seems to be collected by GC, so
if the GC is triggered during the usage of the Concat object, it can be used
some released memory.
This patch rewrite the Concat class without the "luaL_Buffer" system. It uses
"userdata()" forr the memory allocation of the buffer strings.
This patch merges the last imported functions in one, because
the function hlua_metatype is only used by hlua_checudata.
This patch fix also the compilation error became by the
copy of the code.
This patch moves the function hlua_checkudata which check that
an object contains the expected class_reference as metatable.
This function is commonly used by all the lua functions.
The function hlua_metatype is also moved.
When Lua executes functions from its API, these can throws an error.
These function must be executed in a special environment which catch
these error, otherwise a critical error (like segfault) can raise.
This patch add a c file called "hlua_fcn.c" which collect all the
Lua/c function needing safe environment for its execution.
