fix #issue16

[chriskaliX]

I've look into the code of both bcc and data-dog's. Here is the summary:

1. In data-dog‘s way, if a kprobe function name is specific(which means no prefix is needed), it won't be added a prefix dynamically.
2. In bcc, a cache of the text section and weak symbol is used.

In order to not change the way we use(no extra field for kprobe function name specification), I choose the second way(bcc), which will cache data for about 1M, and for sure, we have to run an extra loop to cache the symfile, which I think is acceptable.

[cfc4n]

LGTM.