Rename e{malloc,realloc,free} to u{malloc,realloc,free}, to more obviously

reflect the fact that they allocate and deallocate user memory (i.e.
things reached through a userptr_t).

src/tests/umalloc_test.c

@@ -0,0 +1,26 @@
+#include <vsprintf.h>
+#include <gpxe/uaccess.h>
+#include <gpxe/umalloc.h>
+#include <gpxe/memmap.h>
+
+void umalloc_test ( void ) {
+	struct memory_map memmap;
+	userptr_t bob;
+	userptr_t fred;
+
+	printf ( "Before allocation:\n" );
+	get_memmap ( &memmap );
+
+	bob = ymalloc ( 1234 );
+	bob = yrealloc ( bob, 12345 );
+	fred = ymalloc ( 999 );
+
+	printf ( "After allocation:\n" );
+	get_memmap ( &memmap );
+
+	ufree ( bob );
+	ufree ( fred );
+
+	printf ( "After freeing:\n" );
+	get_memmap ( &memmap );
+}