Slow vipw and fast pwd_mkdb

[Alex Semenyaka]

Hello,

could somebody to comment PR bin/51148? It is suggestion how to pass
a value of cache size to pwd_mkdb when we are doing vipw or such.
It can give a greate speed-up when master.passwd is really big (and
sometimes it is). Appropriate cache size can make process 10 to 100
or more times faster. I gave the results of measurements in that
problem report.

Thanks in advance!

							SY, Alex