[PATCH] Independent shared I/O page limit.

Currently, shared memory pages are used for shared memory cache and
IPC I/O module. Before the change, the number of shared memory pages
needed for IPC I/O was calculated from the size of shared memory
cache. Moreover, shared memory cache was required for IPC I/O.

The patch makes the limit for shared I/O pages independent from the
shared memory cache size and presence. IPC I/O pages limit is
calculated from the number of workers and diskers, it does not depend
on cache_dir configuration. This may change in the future if we learn
how to compute it (e.g., by multiplying max-swap-rate and swap-timeout
if both are available).

---
 src/DiskIO/IpcIo/IpcIoFile.cc |   32 ++++++++++++++++++++++++++++++--
 src/MemStore.cc               |   26 +++++++++++++++++++++++++-
 src/base/RunnersRegistry.h    |    5 +++++
 src/ipc/Queue.cc              |    6 ++++++
 src/ipc/Queue.h               |    3 +++
 src/ipc/mem/Pages.cc          |   38 +++++++++++++-------------------------
 src/ipc/mem/Pages.h           |    3 +++
 src/main.cc                   |    3 +++
 8 files changed, 88 insertions(+), 28 deletions(-)