[dev-context] Add headcommand to floatcaption

[Henri Menke]

Dear Hans,

Could you please add the possibility to switch the headcommand to
floatcaption?  Below you can find a simple patch that implements what I
am proposing.

Happy holidays,
Henri

---

diff --git a/tex/context/base/mkiv/strc-flt.mkvi b/tex/context/base/mkiv/strc-flt.mkvi
index 584cf915f..5b0c2d9e5 100644
--- a/tex/context/base/mkiv/strc-flt.mkvi
+++ b/tex/context/base/mkiv/strc-flt.mkvi
@@ -88,6 +88,7 @@
     \c!minwidth=\v!fit, % id est: the width of the floatbox in some cases
     \c!headstyle=\v!bold,
     \c!headcolor=,
+   \c!headcommand=\hbox,
     \c!leftmargin=\zeropoint,
     \c!rightmargin=\zeropoint,
     \c!outermargin=\zeropoint,
@@ -424,7 +425,8 @@
         \emptyfloatcaptiontrue
       \ifnofloatnumber
       \else
-       \hbox{\usefloatcaptionstyleandcolor\c!headstyle\c!headcolor\thecurrentfloatnumber}%
+       \floatcaptionparameter\c!headcommand
+         {\usefloatcaptionstyleandcolor\c!headstyle\c!headcolor\thecurrentfloatnumber}%
         \ifnofloatcaption \else \ifemptyfloatcaption \else
           \doifelsenothing{\floatcaptionparameter\c!spaceinbetween}
             {\floatcaptionparameter\c!headseparator\relax