loadrevinfo() would fail on a empty log portion due
to a bug in the previous commit.
the loop is supposed to skip all bytes until we encounter
a empty line. the loop starts at the beginning of a line
so when we encounter a \n, we have to terminate, otherwise
read bytes until we see \n (end of a line) and then read
another and test the condition again.
to get the right data size of a file, the revlog needs to have been
opened and the metaheader parsed. as an optimization, we used to
open revlog only on the first read resulting revlogs with metaheaders
having the wrong size returned by fstat() until the first read().
tar relies on fstat() giving the correct file size, so just open
the revlog on open. reading directories can still yield the wrong
size but it is not that critical.
lazily close revlog files and keep up to 8
revlogs arround. also cache the latest extracted
file descriptor of a revision in the revlog.
this avoids the quite expensive reextracting/patching
when we reopen the same file revision.
dont use the racy mktemp()/create, instead create
a uniqueue name and create with OEXCL. this also
avoids a bunch of access() calls.
fix eof case and use pread() in fcopy() to avoid the
seeks.
dont modify changelog temp file but simulate trailing
newline instead.