[analyzer] Don't reinitialize static globals more than once along a path

This patch makes sure that we do not reinitialize static globals when
the function is called more than once along a path. The motivation is
code with initialization patterns that rely on 2 static variables, where
one of them has an initializer while the other does not. Currently, we
reset the static variables with initializers on every visit to the
function along a path.
[analyzer] Add pointer escape type param to checkPointerEscape callback

The checkPointerEscape callback previously did not specify how a
pointer escaped. This change includes an enum which describes the
different ways a pointer may escape. This enum is passed to the
checkPointerEscape callback when a pointer escapes. If the escape
is due to a function call, the call is passed. This changes
previous behavior where the call is passed as NULL if the escape
was due to indirectly invalidating the region the pointer referenced.

A patch by Branden Archer!
[analyzer] Report bugs when freeing memory with offset pointer

The malloc checker will now catch the case when a previously malloc'ed
region is freed, but the pointer passed to free does not point to the
start of the allocated memory. For example:

int *p1 = malloc(sizeof(int));
p1++;
free(p1); // warn

From the "memory.LeakPtrValChanged enhancement to unix.Malloc" entry
in the list of potential checkers.

A patch by Branden Archer!