Bug fixes

1) Fix bug in InfoFlowAnalysis that meant that in a must analysis, the intersection (meet) was not being taken when propagating to another intra-procedural Value*
2) Fix bug in SysCallsAnalysis that led to propagation not occurring if the set of allowed system calls was empty.
3) Fix SysCallsAnalysis so it only outputs an error for a system call if there is some annotation "reaches" the call.
4) Fix CapabilitySysCallsAnalysis so that warnings are produced if annotations are not present. This is because this analysis now does both the work for __soaap_fd_permit and __soaap_limit_fd_syscalls.
5) Fix bugs in test and also add an additional test for assignment to file descriptors