add support for iterating over configure/build/install steps

This allows to easily build 'fat' builds of software package that require multiple configure/build/install iterations, e.g. FFTW providing single/double/long double and quad precision libraries, by simply specifying a **list** of configure options like so:

```python
name = 'FFTW'
version = '3.3.3'

homepage = 'http://www.fftw.org'
description = """FFTW is a C subroutine library for computing the discrete Fourier transform (DFT)
in one or more dimensions, of arbitrary input size, and of both real and complex data."""

toolchain = {'name': 'gompi', 'version': '1.1.0-no-OFED'}
toolchainopts = {'optarch': True, 'pic': True}

sources = ['%s-%s.tar.gz' % (name.lower(), version)]
source_urls = [homepage]

common_configopts = "--with-openmp --with-pic"

configopts = [
              common_configopts + " --enable-single --enable-sse2 --enable-mpi",
              common_configopts + " --enable-long-double --enable-mpi",
              common_configopts + " --enable-quad-precision",
              common_configopts + " --enable-sse2 --enable-mpi",  # default as last
             ]

moduleclass = 'lib'
```