common: Add LIZARDFS_CREATE_EXCEPTION_CLASS_MSG

Add a macro which creates exception class with predefined message, like:

LIZARDFS_CREATE_EXCEPTION_CLASS_MSG(FooException, Exception,
		"Foo happens");
throw FooException();

Change-Id: I924934c0c451535fb993b1fdefdc05e6667cb4b6
master: Add option 'nomasterpermcheck' in mfsexports.cfg

This commit introduces a possibility to disable permission checking in
master server. This feature will be needed in ACL support implementation.

Change-Id: I9970f25ecb38f656fa36d89e6e6b212b94c78ccf
mount: Remove ACL filtering in mount

ACL support was planned to be in MooseFS in future. To prevent using them
unimplemented, ACL have been filtered in xattr. This commit removes this
filter.

Change-Id: I54ee9ce4194060d994be0cf210b0aa7de9a90710
common: Add cfg_get*() functions

This commit introduces new functions:
* cfg_getstring() - for getting std::string instead of char* that must be freed;
* cfg_get() - unified cfg_get<uint32|str|...>() which uses overloading;
* cfg_get<min|max|minmax>value() - cfg_get() with limiting value.

They will be needed for reading e.g. I/O limits configuration.

Change-Id: I10fb8eef4fb2bb09615604918afedb0ae0a3ee62
mount: move and rename IoLimitConfigLoader

Rename IoLimitConfigLoader to IoLimitsConfigLoader (plural "Limits").

Move IoLimitsConfigLoader from mount to common.

Change-Id: Ib77ef3667a9f14b9647f12c1f7fd1664d0cce7ec