Rename varobj_pretty_printed_p to varobj_is_dynamic_p

We think varobj with --available-children-only behaves like a dynamic
varobj, so dyanmic varobj is not pretty-printer specific.  We rename
varobj_pretty_printed_p to varobj_is_dynamic_p, so that we can handle
available-children-only checking in varobj_is_dynamic_p in the next
patch.

gdb:

2014-06-12  Yao Qi  <yao@codesourcery.com>

	* varobj.c (varobj_pretty_printed_p): Rename to ...
	(varobj_is_dynamic_p): ... this.  New function.
	* varobj.h (varobj_pretty_printed_p): Remove declaration.
	(varobj_is_dynamic_p): Declare.
	* mi/mi-cmd-var.c (print_varobj): All callers updated.
	(mi_print_value_p, varobj_update_one): Likewise.