replace collectException(dirEntry()) idiom

[MartinNowak]

• it used exceptions to handle non-exceptional
  situations only to avoid a stat call

NB:
The fact that it can't be done in an optimal way is really an API issue of std.file.dirEntry.

[MartinNowak]

Issue 10240

[andralex]

We must undo this. I've done extensive measurements and stat() calls are REALLY expensive at least on Unixen. Essentially minimizing stat calls in large systems is a sure path to optimization. I am sorry I've pulled this.

[MartinNowak]

In fact this didn't change the number of stat calls (2 per isDir check) because the constructor of DirEntry performs a stat call to enforce that the path exists (https://github.com/D-Programming-Language/phobos/blob/master/std/file.d#L1989) only to do another stat call to find out if it's a directory.
We need to fix Issue 10240.

[andralex]

yah I saw that bug in DirEntry - what a drag