deprecation-related fix in extra_options

well, it was worth a try... ;)

I'll see whether we can lower the level of log messages that (also) got to stdout, but we'll need to clean up some abuse of `log.warning` first...

Examples:

```
== 2014-12-17 01:17:22,919 main.easyconfig.easyconfig WARNING Unable to resolve template value Clang-%(version_major_minor)s-failing-sanitizer-tests.patch with dict {'versionprefix': '', 'versionsuffix': '', 'toolchain_name': 'GCC', 'toolchain_version': '4.8.2'}
== 2014-12-17 01:17:22,919 main.easyconfig.easyconfig WARNING Unable to resolve template value Clang-%(version_major_minor)s-llvm-ar-uid.patch with dict {'versionprefix': '', 'versionsuffix': '', 'toolchain_name': 'GCC', 'toolchain_version': '4.8.2'}
== 2014-12-17 01:17:23,093 main.EB_Clang WARNING Easyconfig does not specify an EasyBuild-version (key 'easybuild_version')! Assuming the latest version
== 2014-12-17 01:17:23,301 main.EB_Clang WARNING Loaded modules detected: ['cluster/delcatty']
== 2014-12-17 01:17:27,476 main.ToolchainOptions WARNING option: option with name _opt_CC returns None
== 2014-12-17 01:17:27,477 main.ToolchainOptions WARNING option: option with name _opt_CXX returns None
== 2014-12-17 01:17:27,477 main.ToolchainOptions WARNING option: option with name _opt_F77 returns None
== 2014-12-17 01:17:27,477 main.ToolchainOptions WARNING option: option with name _opt_F90 returns None
== 2014-12-17 01:17:27,528 main.LinkLibraryPaths WARNING flags_for_subdirs: directory /user/scratch/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge/software/GMP/5.1.3-GCC-4.8.2/lib64 was not found
== 2014-12-17 01:17:27,532 main.LinkLibraryPaths WARNING flags_for_subdirs: directory /user/scratch/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge/software/CLooG/0.18.1-GCC-4.8.2/lib64 was not found
== 2014-12-17 01:17:27,535 main.IncludePaths WARNING flags_for_subdirs: directory /user/scratch/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge/software/CMake/2.8.12-GCC-4.8.2/include was not found
== 2014-12-17 01:17:27,537 main.LinkLibraryPaths WARNING flags_for_subdirs: directory /user/scratch/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge/software/CMake/2.8.12-GCC-4.8.2/lib64 was not found
== 2014-12-17 01:17:27,537 main.LinkLibraryPaths WARNING flags_for_subdirs: directory /user/scratch/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge/software/CMake/2.8.12-GCC-4.8.2/lib was not found
```