common: create directory structure for rpmbuild

rpmbuild version 4.4.2.3 requires to create directory
structure before invoking when _topdir is defined.

Fixes: pmem/issues#3
Merge pull request #22 from plebioda/fix-make-rpm-on-sles11sp3

common: create directory structure for rpmbuild
blk: align ZERO and ERROR bit defs with spec

Thanks to alert reader @stellarhopper for this one!
common: fix _FORTIFY_SOURCE redefinition error

On Gentoo _FORTIFY_SOURCE=2 is defined by default so passing
-D_FORTIFY_SOURCE=2 causes error. Undefining _FORTIFY_SOURCE
and then defining fixes the problem.
Merge pull request #23 from plebioda/fix-fortify-source-on-gentoo

common: fix _FORTIFY_SOURCE redefinition error
tools: pmem-info tool for parsing log and blk pools
tools: add cscope target
tools: update README and pmeminfo(1), add nvml-tools(7)