[gimp] configure, docs: set correct "mypaint-brush-path" value in man page.

[Jehan Pagès <jehanp src gnome org>]

commit 479bcaafdd61c02d329c5a9b09b5bd9896ed79b2
Author: Jehan <jehan girinstud io>
Date:   Thu Mar 29 17:22:15 2018 +0200

    configure, docs: set correct "mypaint-brush-path" value in man page.
    
    This was hard-coded to what I guess was a personal prefix (commit
    368c7c0511), which is obviously wrong. This has to be constructed at
    compilation and the man must mirror whatever is the actual installation
    path of mypaint-brushes package.

 configure.ac     |    4 ++++
 docs/gimprc.5.in |    2 +-
 2 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 8bf725f..9bbc0b8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1667,6 +1667,10 @@ PKG_CHECK_MODULES(LIBMYPAINT, libmypaint >= libmypaint_required_version,,
 PKG_CHECK_MODULES(MYPAINT_BRUSHES, mypaint-brushes-1.0,,
                   [add_deps_error([mypaint-brushes-1.0])])
 
+# We need an autoconf variable for man page construction.
+mypaint_brushes_dir=`$PKG_CONFIG --variable=brushesdir mypaint-brushes-1.0`
+AC_SUBST(mypaint_brushes_dir)
+
 ##################
 # Check for webkit
 ##################
diff --git a/docs/gimprc.5.in b/docs/gimprc.5.in
index fab18ab..b4ee89a 100644
--- a/docs/gimprc.5.in
+++ b/docs/gimprc.5.in
@@ -142,7 +142,7 @@ search.
 This is a colon-separated list of folders to search.
 
 .TP
-(mypaint-brush-path "/local/head/share/mypaint-data/1.0/brushes:~/.mypaint/brushes")
+(mypaint-brush-path "@mypaint_brushes_dir@:~/.mypaint/brushes")
 
 Sets the brush search path.  This is a colon-separated list of folders to
 search.