* app/tools/gimpaligntool.[ch]: improve layout of controls. Add radio buttons allowing selection of reference layer without using Ctrl modifier. Handle removal of target or reference layers from image more correctly. More to come.
* gimp/app/tools/Makefile.am * gimp/app/tools/gimp-tools.c * gimp/app/tools/gimpalignoptions.c * gimp/app/tools/gimpalignoptions.h * gimp/app/tools/gimpaligntool.c * gimp/app/tools/gimpaligntool.h: Add new tool for aligning layers etc, as described in bug #147437. * gimp/app/core/gimpitem.c * gimp/app/core/gimpitem.h (gimp_item_align): add function required by new tool. * gimp/app/core/core-enums.c * gimp/app/core/core-enums.h: add enum for alignment types. * gimp/themes/Default/images/stock-hcenter-24.png * gimp/themes/Default/images/stock-vcenter-24.png * gimp/libgimpwidgets/gimpstock.c * gimp/libgimpwidgets/gimpstock.h * gimp/themes/Default/images/Makefile.am * gimp/themes/Default/images/makefile.msc: add two stock symbols, modeled on the gravity symbols.
