Restore streamInput() performance over PagedBytesReference.

The initial implementation of bulk-reading a streamInput() over PagedBytesReference was slow (byte-by-byte reading when bulk copying).

Times in µs for bulk-reading a stream over plain vs. paged, averaged over 1000 runs:

| MB  | plain µs | paged µs | Ratio |
|----:|---------:|---------:|-------|
|   1 |       72 |     2048 | 28.6  |
|   2 |      140 |     4127 | 29.4  |
|   3 |      218 |     6208 | 28.4  |
|   4 |      430 |     8396 | 19.5  |
|   5 |      700 |    10525 | 15.0  |
|  10 |     1739 |    21055 | 12.1  |
|  20 |     3481 |    42063 | 12.1  |
|  50 |     8701 |   105337 | 12.1  |
| 100 |    17409 |   210848 | 12.1  |

This changeset restores performance:

| MB  | plain µs | paged µs | Ratio |
|----:|---------:|---------:|-------|
|   1 |       65 |       68 | 1.05  |
|   2 |      134 |      141 | 1.04  |
|   3 |      198 |      235 | 1.18  |
|   4 |      456 |      418 | 0.91  |
|   5 |      750 |      761 | 1.01  |
|  10 |     1736 |     1743 | 1.00  |
|  20 |     3514 |     3497 | 0.99  |
|  50 |     8706 |     8700 | 0.99  |
| 100 |    17608 |    17731 | 1.00  |

The performance jitters slightly due to the usual Hotspot variances, OS scheduling etc. For all practical purposes the performance is now back to what it was before.