Extend does not ignore meaningless spaces in pseudoclasses parameters

Pseudoclasses parameters inside extend must match perfectly. The extend expression :extend(:lang( en )) will not match selector without spaces :lang(en).

Sample input:

:lang(en) {
  lang: en;
}
.spacedLang:extend(:lang( en )){}

Actual output:

:lang(en) {
  lang: en;
}

Expected output:

:lang(en),
.spacedLang {
  lang: en;
}

Longer test case with multiple parameters types:

:lang(en) {
  lang: en;
}
:lang( en ) {
  lang: spaced en;
}
.lang:extend(:lang(en)){}
.spacedLang:extend(:lang( en )){}

:nth-child(even) {
    nth: no spaces even;
}
:nth-child( even ) {
    nth: spaces even;
}
.even:extend(:nth-child(even)){}
.spacedEven:extend(:nth-child( even )){}


:nth-child(2n+1) {
    nth: no spaces even;
}
:nth-child(2n + 1) {
    nth: spaces even;
}
.nth:extend(:nth-child(2n+1)){}
.spacedNth:extend(:nth-child(2n + 1)){}

Actual output:

:lang(en),
.lang {
  lang: en;
}
:lang( en ),
.spacedLang {
  lang: spaced en;
}
:nth-child(even),
.even {
  nth: no spaces even;
}
:nth-child( even ),
.spacedEven {
  nth: spaces even;
}
:nth-child(2n+1),
.nth {
  nth: no spaces even;
}
:nth-child(2n + 1),
.spacedNth {
  nth: spaces even;
}

Expected output:

:lang(en),
.lang,
.spacedLang {
  lang: en;
}
:lang( en ),
.lang,
.spacedLang {
  lang: spaced en;
}
:nth-child(even),
.even,
.spacedEven {
  nth: no spaces even;
}
:nth-child( even ),
.even,
.spacedEven {
  nth: spaces even;
}
:nth-child(2n+1),
.nth,
.spacedNth {
  nth: no spaces even;
}
:nth-child(2n + 1),
.nth,
.spacedNth {
  nth: spaces even;
}

Tested on lessc 1.5.0-b3

Start by reproducing the samples with lessc 1.5.0-b3 and compare the actual and expected selector output. Trace the extend handling for pseudoclass parameters, then add coverage for spaces in :lang(), :nth-child(), and arithmetic parameters; done means equivalent parameters match while distinct spaced definitions retain their own declarations.