regexp: make combining chars in collections work #362

Job	Run time
macos (tiny)	1m 22s
macos (normal)	9m 16s
macos (huge)	13m 51s
windows (HUGE, msvc, no, no, x64, stable)	11m 54s
windows (HUGE, mingw, yes, yes, x86, stable, yes)	9m 58s
windows (HUGE, msvc, no, yes, x86)	11m 7s
windows (HUGE, mingw, yes, no, x64, yes)	13m 49s
windows (NORMAL, msvc, yes, no, x86)	6m 56s
windows (NORMAL, mingw, no, yes, x64)	8m 23s
windows (TINY, msvc, yes, yes, x64)	4m 5s
windows (TINY, mingw, no, no, x86)	5m 43s
linux (tiny, clang)	1m 51s
linux (tiny, gcc)	2m 16s
linux (normal, clang)	8m 30s
linux (normal, gcc)	9m 1s
linux (huge, clang)	9m 21s
linux (huge, gcc)	14m 38s
linux (tiny, clang, nogui)	1m 56s
linux (tiny, gcc, nogui)	1m 55s
linux (huge, gcc, uchar, testgui, true, dynamic)	12m 52s
linux (huge, clang, asan, 5.1)	19m 27s
linux (huge, gcc, unittests, true)	2m 37s
linux (normal, gcc, vimtags)	1m 59s
	3h 2m 47s

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