store: optimize fncache._write by direncoding the contents in one go
For a netbeans clone on Windows 7 x64:
Before:
$ hg perffncachewrite
! wall 0.210000 comb 0.218401 user 0.202801 sys 0.015600 (best of 47)
After:
$ hg perffncachewrite
! wall 0.104000 comb 0.109201 user 0.078000 sys 0.031200 (best of 95)
*** 'a\nc\n\n\n\n' 'a\nb\n\n\n'
*** 'a\nb\nc\n' 'a\nc\n'
*** '' ''
*** 'a\nb\nc' 'a\nb\nc'
*** 'a\nb\nc\nd\n' 'a\nd\n'
*** 'a\nb\nc\nd\n' 'a\nc\ne\n'
*** 'a\nb\nc\n' 'a\nc\n'
*** 'a\n' 'c\na\nb\n'
*** 'a\n' ''
*** 'a\n' 'b\nc\n'
*** 'a\n' 'c\na\n'
*** '' 'adjfkjdjksdhfksj'
*** '' 'ab'
*** '' 'abc'
*** 'a' 'a'
*** 'ab' 'ab'
*** 'abc' 'abc'
*** 'a\n' 'a\n'
*** 'a\nb' 'a\nb'
6 6 'y\n\n'
6 6 'y\n\n'
9 9 'y\n\n'
done
done