CCoinsKeyHasher::operator() should return size_t

It currently returns uint64_t, which on older boost (at least 1.46) causes
test failures on 32-bit systems.

This problem was introduced in bc42503.

Fixes #4634.
Added bullet point

To make it easier to add new requirements if necessary
qt: fix unicode character display on osx when building with 10.7 sdk
small net cleanup

- add comment for disabling sigpipe
- add closing comment in compat.h
- remove redundant check in net.h
Merge pull request #4643

292cc07 qt: fix unicode character display on osx when building with 10.7 sdk (Cory Fields)
Merge pull request #4636

efd6b87 small net cleanup (Philip Kaufmann)
[Qt] re-work overviewpage UI

- ensure normal and watch-only stuff looks consistent
- simplify UI by removing unneeded UI layout elements
- change some comments to watch-only from watchonly
Merge pull request #4627

94e1b9e [Qt] re-work overviewpage UI (Philip Kaufmann)
Merge pull request #4635

6c23b08 CCoinsKeyHasher::operator() should return size_t (Wladimir J. van der Laan)
Merge branch 'patch-4' of git://github.com/benhc123/bitcoin into merge-PR4653

Merge #4653