Revert "Work around an obscure bug of the unpickler on Mac OS."

This reverts commit b0defc225bf1dab7f1fb1d35198608e8fd1b88ed.
Work around an unpickler bug on Mac OS (related to lambda?)

This workaround exports the default boot loader (which was
a lambda) into a regular, top-level function. If the bug
was indeed lambda-related, this should fix it properly.
Fixed missing #include in memmanager.hh.
Merge pull request #6 from sjrd/issue/fix-mac-build

Fix the build issue on Mac OS