Modernize FileMgr

• prefer optional over unique_ptr to make a nullable type, and avoid heap-allocation of RootFileHandler and POSIXFileHandler
• better implementation of select1st,select2nd
• prefer value-semantics implementation of get_bit and set_bit

• [2017-11-13 00:03] Validation started with lhcb-future#600
• [2017-11-13 00:04] Validation started with lhcb-future-clang#374
• [2017-11-13 08:05] Validation started with lhcb-gaudi-merge#293
• [2017-11-14 00:02] Validation started with lhcb-future#601
• [2017-11-14 00:03] Validation started with lhcb-future-clang#375
• [2017-11-14 00:03] Validation started with lhcb-gaudi-head#1658

added 1 commit

• 04e8982f - Modernize FileMgr

Compare with previous version

...and aside from this comment about code duplication, I'm fine with this MR.

assigned to @hegner

changed milestone to %v30r0

approved this merge request

resolved all discussions

merged

mentioned in commit 697e2e94

added C++ framework label