Implement filesystem related functions using boost filesystem

[willyd]

Use boost filesystem instead of Unix specific implementations of:

MakeTempFile
MakeTmpDir
mkdir

[bhack]

This will potentially conflict with BVLC#2537

[willyd]

Should we rely on C++14 <filesystem> then?

[bhack]

Yes but you need to investigate what are the minimal g++ clang and msvc version that support that and if this minimal versions are acceptable by core Caffe developers.

[eelstork]

I'm working on this.

[willyd]

@eelstork Great looking forward to try it!

[eelstork]

@willyd does BVLC#3300 answer this?

[willyd]

Yes I will close the issue when I merge these changes.

[eelstork]

@willyd I filed BVLC#3324 which looks related to this. Advising caution.

[willyd]

Closing fixed by: BVLC#3300 and BVLC#3446