nxcomp/src/Loop.cpp: Don't mix using global proxyFD and a local p(roxy)FD variable (in WaitForRemote() and ConnectToRemote()). Rename local variable name.

nxcomp/src/Loop.cpp: Don't reuse global variable names as function parameters in SetupDisplaySocket().

nxcomp/src/Loop.cpp: Avoid duplicate usage of proxyFD (global variable) and *proxyFD (function parameter).

nxcomp/configure.ac,m4/nx-macros.m4,nxcomp/src/Socket.h: Use AC_CHECK_TYPES to detect if type 'in_addr_t' is available.