Reward minors shielded by our pawns / blocking enemy pawns (official-clockwork#372)

Passed STC
```
Test  | minorbehindpawn2
Elo   | 2.83 +- 2.11 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 2.95 (-2.94, 2.94) [0.00, 3.00]
Games | N: 35538 W: 9156 L: 8867 D: 17515
Penta | [370, 4323, 8192, 4416, 468]
```
https://ob.cwchess.org/test/1244/

Passed LTC
```
Test  | minorbehindpawn2
Elo   | 8.93 +- 4.13 (95%)
SPRT  | 40.0+0.40s Threads=1 Hash=64MB
LLR   | 2.95 (-2.94, 2.94) [0.00, 3.00]
Games | N: 7898 W: 1972 L: 1769 D: 4157
Penta | [47, 860, 1933, 1061, 48]
```
https://ob.cwchess.org/test/1247/

Bench: 15454427

Author: TheRealGioviok