Fix check for compression method in rar seek method.
Fix broken RAR seek support.
Using SEEK_CUR or SEEK_END produced the wrong results, SEEK_SET was
fine however. Note that archive_read_data() doesn't function exactly
as POSIX read. Currently, downstreams will have to check the current
file position after after call to archive_read_data() if they are
to use SEEK_CUR afterwards.
Give formats/filters way to know data amount requested from archive_read_data().
Update RAR test case to expect correct results from calls to archive_read_data().
Fix build failure when doing normal builds.
These are builds done running a standard './configure && make'. This
will also fix a corner case where the whence is set to anything other than
SEEK_SET, SEEK_CUR, or SEEK_END. The behavior is to use SEEK_SET by default.
Fix check for EOF in RAR format reader.
Add checks for proper return value reading past EOF in RAR archives.
Change how seek support in stored RARs are handled.
This fixes various test cases when seeking is used.
Add new tests in multivolume RAR seek test case.
Add new test case to thouroughly test multivolume RAR seek support.
Write common checks for files in a separate function.
Remove error about unreachable code, fixes build on Visual Studio 12.
Fix build errors on Visual Studio from negating value of sizeof operator.
Support POSIX regular expression support using PCRE in CMake builds.

This change is mainly meant for Windows regex support, where PCRE Windows development is much
more active than development of the regex library found in the GNUWin32 packages. I found that
the latest release of PCRE built right out of the box, unlike the GNUWin32 regex library released
6 years ago which failed to build from source for me using the mingw toolchain.
Add CMake option to explicitly enable/disable /SAFESEH linker flag for Visual Studio builds.

Visual Studio 12 enables this option by default. Enabling /SAFESEH will produce build failures when
attempting to link other libraries which were not built with /SAFESEH. This would typically be
the case for libraries built using the mingw toolchain, where the option to use structured exception
handling is not yet available.

The option is used as follows.
  Setting to "YES" sets "/SAFESEH" linker flag
  Setting to "NO" sets "/SAFESEH:NO" linker flag
  Setting to any other value such as "AUTO" won't do anything (set the default linker flag from Visual Studio)
Rename PCREPOSIX_INCLUDE* to PCRE_INCLUDE* as pcreposix.h will be found alongside pcre.h.
Minor formatting change, no functional change.
Redo check for pcreposix library.

Other check was broken, it did not set PCRE_STATIC when necessary nor did it add needed PCREPOSIX_LIBRARIES
for Visual Studio build.
Add check for build without PCRE_STATIC defined.
Check that build did not succeed with WITHOUT_PCRE_STATIC before defining PCRE_STATIC.