Restore copyMatchTry4

[lizthegrey]

Fixes #205

cortex a72:

benchmark                        old ns/op     new ns/op     delta
BenchmarkUncompress-16           20.8          20.8          +0.00%
BenchmarkUncompressPg1661-16     1702946       1585558       -6.89%
BenchmarkUncompressDigits-16     124267        111448        -10.32%
BenchmarkUncompressTwain-16      1177542       1002623       -14.85%
BenchmarkUncompressRand-16       9120          9116          -0.04%

benchmark                        old MB/s     new MB/s     speedup
BenchmarkUncompressPg1661-16     221.60       238.00       1.07x
BenchmarkUncompressDigits-16     766.77       854.96       1.12x
BenchmarkUncompressTwain-16      217.74       255.73       1.17x
BenchmarkUncompressRand-16       1798.55      1799.46      1.00x

benchmark                        old allocs     new allocs     delta
BenchmarkUncompress-16           0              0              +0.00%
BenchmarkUncompressPg1661-16     4              4              +0.00%
BenchmarkUncompressDigits-16     4              4              +0.00%
BenchmarkUncompressTwain-16      4              4              +0.00%
BenchmarkUncompressRand-16       4              4              +0.00%

benchmark                        old bytes     new bytes     delta
BenchmarkUncompress-16           0             0             +0.00%
BenchmarkUncompressPg1661-16     184           184           +0.00%
BenchmarkUncompressDigits-16     184           210           +14.13%
BenchmarkUncompressTwain-16      186           186           +0.00%
BenchmarkUncompressRand-16       187           186           -0.53%

ampere:

benchmark                       old ns/op     new ns/op     delta
BenchmarkUncompress-4           8.84          8.86          +0.25%
BenchmarkUncompressPg1661-4     946111        910414        -3.77%
BenchmarkUncompressDigits-4     62239         60205         -3.27%
BenchmarkUncompressTwain-4      599464        576336        -3.86%
BenchmarkUncompressRand-4       4250          4485          +5.53%

benchmark                       old MB/s     new MB/s     speedup
BenchmarkUncompressPg1661-4     398.86       414.50       1.04x
BenchmarkUncompressDigits-4     1530.93      1582.66      1.03x
BenchmarkUncompressTwain-4      427.72       444.88       1.04x
BenchmarkUncompressRand-4       3859.74      3657.60      0.95x

benchmark                       old allocs     new allocs     delta
BenchmarkUncompress-4           0              0              +0.00%
BenchmarkUncompressPg1661-4     4              4              +0.00%
BenchmarkUncompressDigits-4     4              4              +0.00%
BenchmarkUncompressTwain-4      4              4              +0.00%
BenchmarkUncompressRand-4       4              4              +0.00%

benchmark                       old bytes     new bytes     delta
BenchmarkUncompress-4           0             0             +0.00%
BenchmarkUncompressPg1661-4     184           184           +0.00%
BenchmarkUncompressDigits-4     184           184           +0.00%
BenchmarkUncompressTwain-4      184           184           +0.00%
BenchmarkUncompressRand-4       184           184           +0.00%

[lizthegrey]

Tests pass if bc1239b is reverted. This failure predates my change.