Fix compiler errors

• Update autoconf configuration
• Use c++ compiler instead of g++
• Remove .h from stream includes
• Remove unneeded class qualifier
• Remove duplicate default function argument
• Fix missing argument in exit
• Add string cast for operator<<
• Add missing include in mergeunit
• Remove unnecessary pointer cast in indexer
• Use std namespace
• Remove -fwritable-strings compiler option
• Fix NULL character type error
• Remove deprecated register keyword