scan.coverity: improve the modeling file of git.git

Hi Sam, John and Jeff,

I'm writing to you, as you're listed as the administrator of the git.git project on scan.coverity.com

We're currently seeing lots of false positives as the xmalloc/xrealloc function is handled not properly by coverity. There are lots of errors "Allocation too small for type"

Quoting (starting linenumbers are code) from some xrealloc ocurrence:

 95void *xrealloc(void *ptr, size_t size)
 96{
 97        void *ret;
 98
 99        memory_limit_check(size);
100        ret = realloc(ptr, size);

1. Condition "!ret", taking true branch   
2. Condition "!size", taking true branch

101        if (!ret && !size)
   
3. buffer_alloc: "realloc(void *, size_t)" which allocates 1 bytes based on "1UL".   
4. var_assign: Assigning: "ret" = storage allocated by "realloc(ptr, 1UL)".

102                ret = realloc(ptr, 1);
   
5. Condition "!ret", taking false branch

103        if (!ret) {
104                try_to_free_routine(size);
105                ret = realloc(ptr, size);
106                if (!ret && !size)
107                        ret = realloc(ptr, 1);
108                if (!ret)
109                        die("Out of memory, realloc failed");
110        }
   
6. return_dbuffer: Returning allocated array "ret".

111 return ret; 112}

However I have reviewed the function and I'd be pretty sure it would work as expected. According to https://scan.coverity.com/tune we can upload a modelling file, which will allow us to supress such false positive errors. I believe we'd need to put in the modelling file something like:

	// coverity[+alloc]
	void *xrealloc(void *ptr, size_t size);

and that should do. We'd not need to modify the git.git sources, but just add such a declaration to the modelling file.

Does anyone of you administrators want to experiment with that?

Cheers, Stefan