• fix RT#75727 - after's XS implementation call XSRETURN(-1) when it
  doesn't find an element (2nd patch provided by Reini Urban,
  regression test provided by Tony Cook)
  
• fix RT#113117 - XS's minmax() sometimes return undef (perl >= 5.20),
  thanks PERLANCAR and SREZIC
  
• explicit test for thesis in RT#110998 - XS implementation of pairwise
  fails with memory allocation error when there are more return values
  than in original lists -- thesis is proven wrong
  
• efficiency improvements by bulk88
  
• improve some tests to get clearer reports
  
• distinguish between "Makefile.PL find's a .git directory" and
  "Makefile.PL runs in maintainer mode"