implement "low hanging fruit" from C11

based on Gregor's patch sent to the list. includes:
- stdalign.h
- removing gets in C11 mode
- adding aligned_alloc and adjusting other functions to use it
- adding 'x' flag to fopen for exclusive mode

include/stdlib.h

@@ -38,6 +38,7 @@ void *malloc (size_t);
 void *calloc (size_t, size_t);
 void *realloc (void *, size_t);
 void free (void *);
+void *aligned_alloc(size_t alignment, size_t size);
 
 void abort (void);
 int atexit (void (*) (void));